Mortgage Servicing Rights - Changes in Fair Value of Capitalized MSRs (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Transfers and Servicing of Financial Assets [Abstract]
Balance at beginning of period	$ 2,582	$ 2,056	$ 2,591	$ 2,512
Rights purchased	4	18	10	32
Rights capitalized	115	142	319	372
Changes in fair value of MSRs
Due to fluctuations in market interest rates	(12)	42	(42)	(446)
Due to revised assumptions or models	1		18
Other changes in fair value	(92)	(127)	(298)	(339)
Balance at end of period	$ 2,598	$ 2,131	$ 2,598	$ 2,131