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Long-Term Debt - Additional Information (Detail) - USD ($)
$ in Millions
Dec. 31, 2016
Dec. 31, 2015
Debt Instrument [Line Items]    
Notes and debentures that mature in 2017 $ 750  
Notes and debentures that mature in 2018 3,600  
Notes and debentures that mature in 2019 4,200  
Notes and debentures that mature in 2020 4,000  
Notes and debentures that mature in 2021 4,300  
Carrying value 3,542 $ 2,552
Series A Preferred Stock    
Debt Instrument [Line Items]    
Carrying value 500 $ 500
Mellon Capital I V | Series A Preferred Stock    
Debt Instrument [Line Items]    
Carrying value $ 500