Mortgage Servicing Rights - Changes in Fair Value of Capitalized MSRs (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Transfers and Servicing of Financial Assets [Abstract]
Balance at beginning of period	$ 2,512	$ 2,338
Rights purchased	9	6
Rights capitalized	99	145
Changes in fair value of MSRs
Due to fluctuations in market interest rates	(301)	(131)
Other changes in fair value	(97)	(108)
Balance at end of period	$ 2,222	$ 2,250