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Mortgage Servicing Rights - Changes in Fair Value of Capitalized MSRs (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Transfers and Servicing of Financial Assets [Abstract]      
Balance at beginning of period $ 2,512 $ 2,338 $ 2,680
Rights purchased 43 29 5
Rights capitalized 524 632 382
Rights sold     (141)
Changes in fair value of MSRs      
Due to fluctuations in market interest rates (55) (58) (276)
Due to revised assumptions or models 19 10 86
Other changes in fair value (452) (439) (398)
Balance at end of period $ 2,591 $ 2,512 $ 2,338