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Preferred Stock - Additional Information (Detail) - USD ($)
$ / shares in Units, $ in Millions
6 Months Ended
Jun. 30, 2017
Dec. 31, 2016
Class of Stock [Line Items]    
Number of preferred stock, shares authorized 50,000,000 50,000,000
Issuance costs of redeemed preferred stock $ (10)  
Series J [Member]    
Class of Stock [Line Items]    
Preferred Stock, Shares Issued 40,000  
Liquidation preference per share $ 25,000  
Preferred stock dividend rate fixed percentage 5.30%  
Preferred stock dividend rate variable percentage 2.914%  
Redemption period of preferred stock 90 days  
Preferred stock redemption rate Apr. 15, 2027  
Series G [Member]    
Class of Stock [Line Items]    
Issuance costs of redeemed preferred stock $ (10)