Goodwill and Mortgage Servicing Rights - Mortgage Servicing Rights (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Mortgage servicing rights activity [Abstract]
Fair value at beginning of period	$ 3,276	$ 4,699
MSR activity:
Originations of MSRs	404	271
Purchase of MSRs	179	2
Disposition of MSRs	1	(75)
Net additions/(dispositions)	584	198
Changes due to collection/realization of expected cash flows	(187)	(248)
Changes in valuation due to inputs and assumptions:
Changes due to market interest rates and other	836	(1,370)
Changes in valuation due to other inputs and assumptions:
Projected cash flows (e.g., cost to service)	(24)	(1)
Discount rates	0	0
Prepayment model changes and other	(15)	(11)
Total changes in valuation due to other inputs and assumptions	(39)	(12)
Total changes in valuation due to inputs and assumptions	797	(1,382)
Fair value at end of period	4,470	3,267
Changes in unrealized gains/(losses) included in income related to MSRs	797	(1,382)
Contractual service fees, late fees and other ancillary fees included in income	291	364
Third-party mortgage loans serviced	444,000	506,000
Servicer advances, net of an allowance for uncollectible amounts	$ 1,800	$ 1,700