Annual report pursuant to Section 13 and 15(d)

Employee Benefit Plans - Fair Value Measurements (Details)

v3.8.0.1
Employee Benefit Plans - Fair Value Measurements (Details) - USD ($)
$ in Millions
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets $ 25,675 $ 23,772    
Level 1        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 13,332 12,483    
Level 2        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 11,251 10,260    
Level 3        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 1,092 1,029 $ 1,037 $ 962
Money market and interest-bearing cash        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 2,190 776    
Money market and interest-bearing cash | Level 1        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 2,190 776    
Money market and interest-bearing cash | Level 2        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 0 0    
Money market and interest-bearing cash | Level 3        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 0 0    
Cash and cash equivalent commingled/mutual funds        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 1,004 997    
Cash and cash equivalent commingled/mutual funds | Level 1        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 0 0    
Cash and cash equivalent commingled/mutual funds | Level 2        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 1,004 997    
Cash and cash equivalent commingled/mutual funds | Level 3        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 0 0    
U.S. government and agency securities        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 4,194 3,951    
U.S. government and agency securities | Level 1        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 3,331 3,125    
U.S. government and agency securities | Level 2        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 854 816    
U.S. government and agency securities | Level 3        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 9 10 11 11
Corporate debt securities        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 2,417 1,892    
Corporate debt securities | Level 1        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 0 0    
Corporate debt securities | Level 2        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 2,417 1,892    
Corporate debt securities | Level 3        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 0 0    
Asset-backed securities        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 1,832 2,246    
Asset-backed securities | Level 1        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 0 0    
Asset-backed securities | Level 2        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 1,832 2,246    
Asset-backed securities | Level 3        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 0 0    
Non-U.S. debt securities        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 1,591 1,494    
Non-U.S. debt securities | Level 1        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 693 789    
Non-U.S. debt securities | Level 2        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 898 705    
Non-U.S. debt securities | Level 3        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 0 0    
Fixed income commingled/mutual funds        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 2,451 2,281    
Fixed income commingled/mutual funds | Level 1        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 775 778    
Fixed income commingled/mutual funds | Level 2        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 1,676 1,503    
Fixed income commingled/mutual funds | Level 3        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 0 0    
Common and preferred equity securities        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 5,833 6,120    
Common and preferred equity securities | Level 1        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 5,833 6,120    
Common and preferred equity securities | Level 2        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 0 0    
Common and preferred equity securities | Level 3        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 0 0    
Equity commingled/mutual funds        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 2,024 1,960    
Equity commingled/mutual funds | Level 1        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 271 735    
Equity commingled/mutual funds | Level 2        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 1,753 1,225    
Equity commingled/mutual funds | Level 3        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 0 0    
Public real estate investment trusts        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 138 145    
Public real estate investment trusts | Level 1        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 138 145    
Public real estate investment trusts | Level 2        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 0 0    
Public real estate investment trusts | Level 3        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 0 0    
Private real estate        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 93 150    
Private real estate | Level 1        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 0 0    
Private real estate | Level 2        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 0 0    
Private real estate | Level 3        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 93 150 144 127
Real estate commingled/mutual funds        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 844 760    
Real estate commingled/mutual funds | Level 1        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 0 0    
Real estate commingled/mutual funds | Level 2        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 13 12    
Real estate commingled/mutual funds | Level 3        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 831 748 731 632
Limited partnerships        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 240 170    
Limited partnerships | Level 1        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 0 0    
Limited partnerships | Level 2        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 155 132    
Limited partnerships | Level 3        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 85 38 49 65
Other investments        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 824 830    
Other investments | Level 1        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 101 15    
Other investments | Level 2        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 649 732    
Other investments | Level 3        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 74 83 $ 102 $ 127
Interest Rate Swap        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 156 257    
Participant Loans        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 20 36    
Commodity and Balanced Funds        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets 451 369    
Other Various Investments        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets $ 197 $ 168