Annual report pursuant to Section 13 and 15(d)

Employee Benefit Plans - Level 3 Fair Value Measurements (Details)

v3.10.0.1
Employee Benefit Plans - Level 3 Fair Value Measurements (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Change in fair value of plan assets      
Fair value, January 1 $ 25,675    
Fair value, December 31 23,475 $ 25,675  
U.S. government and agency securities      
Change in fair value of plan assets      
Fair value, January 1 4,194    
Fair value, December 31 4,451 4,194  
Private real estate      
Change in fair value of plan assets      
Fair value, January 1 93    
Fair value, December 31 5 93  
Real estate commingled/mutual funds      
Change in fair value of plan assets      
Fair value, January 1 844    
Fair value, December 31 898 844  
Limited partnerships      
Change in fair value of plan assets      
Fair value, January 1 240    
Fair value, December 31 240 240  
Other investments      
Change in fair value of plan assets      
Fair value, January 1 824    
Fair value, December 31 1,045 824  
Level 3      
Change in fair value of plan assets      
Fair value, January 1 1,092 1,029 $ 1,037
Actual Return on Plan Assets Still Held at the Reporting Date 33 90 24
Purchases, Sales and Settlements 444 (27) (32)
Fair value, December 31 1,569 1,092 1,029
Level 3 | U.S. government and agency securities      
Change in fair value of plan assets      
Fair value, January 1 9 10 11
Actual Return on Plan Assets Still Held at the Reporting Date 0 0 0
Purchases, Sales and Settlements 0 (1) (1)
Fair value, December 31 9 9 10
Level 3 | Private real estate      
Change in fair value of plan assets      
Fair value, January 1 93 150 144
Actual Return on Plan Assets Still Held at the Reporting Date (7) 8 1
Purchases, Sales and Settlements (81) (65) 5
Fair value, December 31 5 93 150
Level 3 | Real estate commingled/mutual funds      
Change in fair value of plan assets      
Fair value, January 1 831 748 731
Actual Return on Plan Assets Still Held at the Reporting Date 52 63 21
Purchases, Sales and Settlements 2 20 (4)
Fair value, December 31 885 831 748
Level 3 | Limited partnerships      
Change in fair value of plan assets      
Fair value, January 1 85 38 49
Actual Return on Plan Assets Still Held at the Reporting Date (12) 14 (2)
Purchases, Sales and Settlements 9 33 (9)
Fair value, December 31 82 85 38
Level 3 | Other investments      
Change in fair value of plan assets      
Fair value, January 1 74 83 102
Actual Return on Plan Assets Still Held at the Reporting Date 0 5 4
Purchases, Sales and Settlements 514 (14) (23)
Fair value, December 31 $ 588 $ 74 $ 83