Fair Value Measurements - Reconciliation of Assets and Liabilities Measured at Fair Value on a Recurring Basis Using Significant Unobservable Inputs (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation
Derivative assets	$ 2,919	$ 1,673
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
Balance, beginning of period	1,023	991	$ 861
Included in earnings	(393)	(339)	(73)
Purchases/originations	232	428	158
Settlements	(242)	(93)	(19)
Transfers into Level 3	49	36	64
Balance, end of period	669	1,023	991
The amount of total (losses) gains for the period included in earnings attributable to the change in unrealized gains or losses relating to instruments still held	(269)	(338)	(57)
Fair value, recurring
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation
Derivative assets	2,919	1,673
Derivative liabilities	1,072	741
Fair value, recurring \| Level 3
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation
Derivative assets	61	18
Derivative liabilities	209	171
Interest Rate Contract \| Fair value, recurring
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation
Derivative assets	2,289	1,237
Derivative liabilities	285	157
Interest Rate Contract \| Fair value, recurring \| Level 3
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation
Derivative assets	61	18	7
Derivative liabilities	8	8	8
Residential Mortgage Loans
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
Balance, beginning of period	183	179	137
Included in earnings	3	(1)	(3)
Purchases/originations	0	0	0
Settlements	(74)	(31)	(19)
Transfers into Level 3	49	36	64
Balance, end of period	161	183	179
The amount of total (losses) gains for the period included in earnings attributable to the change in unrealized gains or losses relating to instruments still held	3	(1)	(3)
Servicing Rights
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
Balance, beginning of period	993	938	858
Included in earnings	(565)	(376)	(83)
Purchases/originations	228	431	163
Settlements	0	0	0
Transfers into Level 3	0	0	0
Balance, end of period	656	993	938
The amount of total (losses) gains for the period included in earnings attributable to the change in unrealized gains or losses relating to instruments still held	(227)	(250)	(4)
Interest Rate Contract
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
Balance, beginning of period	10	(1)	3
Included in earnings	272	145	72
Purchases/originations	4	(3)	(5)
Settlements	(233)	(131)	(71)
Transfers into Level 3	0	0	0
Balance, end of period	53	10	(1)
The amount of total (losses) gains for the period included in earnings attributable to the change in unrealized gains or losses relating to instruments still held	58	20	9
Equity Derivatives
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
Balance, beginning of period	(163)	(125)	(137)
Included in earnings	(103)	(107)	(59)
Purchases/originations	0	0	0
Settlements	65	69	71
Transfers into Level 3	0	0	0
Balance, end of period	(201)	(163)	(125)
The amount of total (losses) gains for the period included in earnings attributable to the change in unrealized gains or losses relating to instruments still held	$ (103)	$ (107)	$ (59)

Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Amount of unrealized gain (loss) recognized in income from asset measured at fair value on recurring basis using unobservable input (level 3) and still held.

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Amount of gain (loss) recognized in income from asset measured at fair value on recurring basis using unobservable input (level 3).

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Amount of purchases of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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