Mortgage Servicing Rights - Changes in Fair Value of Capitalized MSRs (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Transfers and Servicing of Financial Assets [Abstract]
Balance at beginning of period	$ 1,887	$ 2,656	$ 2,546	$ 2,791
Rights purchased	3	6	8	7
Rights capitalized	190	127	391	205
Rights sold	1		2
Changes in fair value of MSRs
Due to fluctuations in market interest rates	(64)	(211)	(807)	(330)
Due to revised assumptions or models	27	4	44	15
Other changes in fair value	(204)	(124)	(344)	(230)
Balance at end of period	$ 1,840	$ 2,458	$ 1,840	$ 2,458