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Mortgage Servicing Rights - Changes in Fair Value of Capitalized MSRs (Detail) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Transfers and Servicing of Financial Assets [Abstract]    
Balance at beginning of period $ 2,645 $ 2,591
Rights purchased 2 2
Rights capitalized 100 122
Changes in fair value of MSRs    
Due to fluctuations in market interest rates 114 20
Due to revised assumptions or models 24 12
Other changes in fair value (105) (105)
Balance at end of period $ 2,780 $ 2,642