Mortgage Servicing Rights - Changes in Fair Value of Capitalized MSRs (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Transfers and Servicing of Financial Assets [Abstract]
Balance at beginning of period	$ 1,840	$ 2,458	$ 2,546	$ 2,791
Rights purchased	8	6	16	13
Rights capitalized	321	168	712	373
Rights sold	1	4	3	4
Changes in fair value of MSRs
Due to fluctuations in market interest rates	(8)	(243)	(815)	(573)
Due to revised assumptions or models	(7)	15	37	30
Other changes in fair value	(177)	(112)	(521)	(342)
Balance at end of period	$ 1,978	$ 2,296	$ 1,978	$ 2,296