Annual report pursuant to Section 13 and 15(d)

Shareholders' Equity - Preferred Stock Narrative (Details)

v3.8.0.1
Shareholders' Equity - Preferred Stock Narrative (Details)
$ / shares in Units, $ in Millions
 12 Months Ended
Dec. 31, 2017
USD ($)
d
quarterly_period
semi_annual_period
director
$ / shares
shares
Dec. 31, 2016
USD ($)
$ / shares
Dec. 31, 2015
USD ($)
Class of Stock [Line Items]      
Preferred stock dividends | $ $ 1,578 $ 1,682 $ 1,483
Preferred stock, par value (in dollars per share) | $ / shares $ 0.01 $ 0.01  
Series L Preferred Stock      
Class of Stock [Line Items]      
Per annum dividend rate 7.25%    
Preferred stock to be convertible into common shares (in shares) | shares 20    
Number of trading days | d 20    
Period of consecutive trading days | d 30    
Threshold percentage of common stock closing price (exceeds) 130.00%    
Preferred Stock, Excluding Series B, F, G and T Preferred      
Class of Stock [Line Items]      
Number of semi annual periods in arrears (or more) | semi_annual_period 3    
Number of quarterly periods in arrears (or more) | quarterly_period 6    
Number of additional directors to be elected | director 2    
Number of semi annual periods for termination (or more) | semi_annual_period 2    
Number of quarterly periods for termination (or more) | quarterly_period 4    
Retained Earnings      
Class of Stock [Line Items]      
Preferred stock dividends | $ $ 1,578 $ 1,682 $ 1,483