Mortgage Servicing Rights - Changes in Fair Value of Capitalized MSRs (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Transfers and Servicing of Financial Assets [Abstract]
Balance at beginning of period	$ 2,591	$ 2,512
Rights purchased	2	8
Rights capitalized	122	99
Changes in fair value of MSRs
Due to fluctuations in market interest rates	20	(301)
Due to revised assumptions or models	12
Other changes in fair value	(105)	(96)
Balance at end of period	$ 2,642	$ 2,222