Mortgage Servicing Rights - Changes in Fair Value of Capitalized MSRs (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Transfers and Servicing of Financial Assets [Abstract]
Balance at beginning of period	$ 2,056	$ 2,481	$ 2,512	$ 2,338
Rights purchased	18	7	32	22
Rights capitalized	142	182	372	491
Changes in fair value of MSRs
Due to fluctuations in market interest rates	42	(168)	(446)	(127)
Due to revised assumptions or models		7		9
Other changes in fair value	(127)	(112)	(339)	(336)
Balance at end of period	$ 2,131	$ 2,397	$ 2,131	$ 2,397