Fair Value Measurements - Reconciliation of Assets and Liabilities Measured at Fair Value on a Recurring Basis Using Significant Unobservable Inputs (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation
Derivative assets	$ 3,934		$ 3,934		$ 2,862
Derivative liabilities	2,738		2,738		$ 1,072
Unrealized gains or losses included in other comprehensive income for instruments still held	0	$ 0	0	$ 0
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
Balance, beginning of period	787	767	669	1,023
Total (losses) gains (realized/unrealized) included in earnings	(17)	(38)	(27)	(349)
Purchases/originations	169	55	380	190
Settlements	(50)	(64)	(153)	(173)
Transfers into Level 3	18	10	38	39
Balance, end of period	907	730	907	730
The amount of total gains (losses) for the period included in earnings attributable to the change in unrealized gains or losses relating to assets still held	27	37	37	(264)
Interest rate contracts | Level 3
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation
Derivative assets	27	92	27	92
Derivative liabilities	8	8	8	8
Servicing Rights
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
Balance, beginning of period	818	676	656	993
Total (losses) gains (realized/unrealized) included in earnings	(44)	(71)	(95)	(519)
Purchases/originations	169	55	382	186
Settlements	0	0	0	0
Transfers into Level 3	0	0	0	0
Balance, end of period	943	660	943	660
The amount of total gains (losses) for the period included in earnings attributable to the change in unrealized gains or losses relating to assets still held	19	(2)	77	(281)
Interest rate contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
Balance, beginning of period	31	89	53	10
Total (losses) gains (realized/unrealized) included in earnings	44	55	136	241
Purchases/originations	0	0	(2)	4
Settlements	(56)	(60)	(168)	(171)
Transfers into Level 3	0	0	0	0
Balance, end of period	19	84	19	84
The amount of total gains (losses) for the period included in earnings attributable to the change in unrealized gains or losses relating to assets still held	25	61	28	88
Equity Derivatives
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
Balance, beginning of period	(213)	(183)	(201)	(163)
Total (losses) gains (realized/unrealized) included in earnings	(17)	(22)	(67)	(73)
Purchases/originations	0	0	0	0
Settlements	19	17	57	48
Transfers into Level 3	0	0	0	0
Balance, end of period	(211)	(188)	(211)	(188)
The amount of total gains (losses) for the period included in earnings attributable to the change in unrealized gains or losses relating to assets still held	(17)	(22)	(67)	(73)
Residential Mortgage Loans
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
Balance, beginning of period	151	185	161	183
Total (losses) gains (realized/unrealized) included in earnings	0	0	(1)	2
Purchases/originations	0	0	0	0
Settlements	(13)	(21)	(42)	(50)
Transfers into Level 3	18	10	38	39
Balance, end of period	156	174	156	174
The amount of total gains (losses) for the period included in earnings attributable to the change in unrealized gains or losses relating to assets still held	$ 0	$ 0	$ (1)	$ 2