Fair Value (Reconciliation of Recurring Fair Value Measurements) (Details) - Fair Value, Measurements, Recurring - Level 3 - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ 5,395	$ 6,157
Included in Earnings	(255)	89
Included in Other comprehensive income (b)	(94)	12
Purchases	781	769
Sales	(231)	(662)
Issuances	145	89
Settlements	(612)	(1,027)
Transfers into Level 3	112	16
Transfers out of Level 3	(104)	(48)
Ending Balance	5,137	5,395
Unrealized gains (losses) on assets held on Consolidated Balance Sheet	(301)	(163)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	344	333
Included in Earnings	206	169
Purchases		16
Sales	4	12
Issuances	124	133
Settlements	(360)	(319)
Ending Balance	318	344
Unrealized gains or (losses) on liabilities held on Consolidated Balance Sheet	187	161
Fair Value Additional Information [Abstract]
Net gains (losses) included in earnings (realized and unrealized) relating to Level 3 assets and liabilities	(461)	(80)
Net unrealized gains (losses) relating to Level 3 assets and liabilities	(488)	(324)
Loans Held For Sale \| Residential Mortgages
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	2	2
Included in Earnings	(1)
Purchases	124	5
Sales	(13)	(2)
Settlements	(21)	(2)
Transfers into Level 3	93	16
Transfers out of Level 3	(21)	(17)
Ending Balance	163	2
Unrealized gains (losses) on assets held on Consolidated Balance Sheet	(1)
Loans Held For Sale \| Commercial Mortgages
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	64	87
Included in Earnings	(2)	1
Settlements	(5)	(24)
Ending Balance	57	64
Unrealized gains (losses) on assets held on Consolidated Balance Sheet	(2)	1
Securities available for sale
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	2,055	2,486
Included in Earnings	60	80
Included in Other comprehensive income (b)	(94)	12
Purchases	4	9
Sales		(3)
Settlements	(397)	(529)
Transfers into Level 3	19
Transfers out of Level 3
Ending Balance	1,647	2,055
Securities available for sale \| Residential mortgage-backed Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	1,741	2,128
Included in Earnings	53	73
Included in Other comprehensive income (b)	(75)	15
Settlements	(354)	(475)
Ending Balance	1,365	1,741
Securities available for sale \| Commercial mortgage- backed non-agency
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance
Included in Other comprehensive income (b)	(8)
Transfers into Level 3	19
Ending Balance	11
Securities available for sale \| Asset-backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	240	274
Included in Earnings	6	6
Included in Other comprehensive income (b)	(7)	3
Settlements	(40)	(43)
Ending Balance	199	240
Securities available for sale \| Other debt
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	74	84
Included in Earnings	1	1
Included in Other comprehensive income (b)	(4)	(6)
Purchases	4	9
Sales		(3)
Settlements	(3)	(11)
Ending Balance	72	74
Loans
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	300	272
Included in Earnings	28	13
Purchases	161	142
Sales	(39)	(42)
Settlements	280	(54)
Transfers out of Level 3	(83)	(31)
Ending Balance	647	300
Unrealized gains (losses) on assets held on Consolidated Balance Sheet	28	7
Equity investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	1,276	1,255
Included in Earnings	(63)	262
Purchases	229	374
Sales	(179)	(615)
Ending Balance	1,263	1,276
Unrealized gains (losses) on assets held on Consolidated Balance Sheet	(69)	57
Mortgage Servicing Rights \| Residential Mortgages
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	995	1,257
Included in Earnings	(377)	(250)
Purchases	208	114
Issuances	45	36
Settlements	(198)	(162)
Ending Balance	673	995
Unrealized gains (losses) on assets held on Consolidated Balance Sheet	(377)	(235)
Mortgage Servicing Rights \| Commercial Mortgages
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	649	726
Included in Earnings	(109)	(87)
Purchases	44	103
Issuances	100	53
Settlements	(115)	(146)
Ending Balance	569	649
Unrealized gains (losses) on assets held on Consolidated Balance Sheet	(109)	(87)
Trading securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance		2
Settlements		(2)
Ending Balance
Financial derivatives
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	54	25
Included in Earnings	209	70
Purchases	11	22
Settlements	(156)	(63)
Ending Balance	118	54
Unrealized gains (losses) on assets held on Consolidated Balance Sheet	229	94
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	200	268
Included in Earnings	189	101
Sales	4	10
Settlements	(120)	(179)
Ending Balance	273	200
Unrealized gains or (losses) on liabilities held on Consolidated Balance Sheet	186	112
Other assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance		45
Settlements		(45)
Ending Balance
Other borrowed funds
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	7	7
Issuances	28	52
Settlements	(33)	(52)
Ending Balance	2	7
Other liabilities
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	137	58
Included in Earnings	17	68
Purchases		16
Sales		2
Issuances	96	81
Settlements	(207)	(88)
Ending Balance	43	137
Unrealized gains or (losses) on liabilities held on Consolidated Balance Sheet	$ 1	$ 49

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This item represents the amount of the net change in unrealized (holding) gains or losses for the period which are included in the statement of income. Such unrealized (holding) gains or losses relate to those assets and liabilities still held at the reporting date for which fair value is measured on a recurring basis using significant unobservable inputs (Level 3).

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This element represents net gains or losses for the period (realized and unrealized), arising from assets and liabilities measure at fair value on a recurring basis using unobservable inputs (Level 3), which are included in earnings or resulted in a change in net asset value.

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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 unrealized gain (loss) recognized in income from liability 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 gain (loss) recognized in other comprehensive income (OCI) from asset measured at fair value on recurring basis using unobservable input (level 3).

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Amount of issuances 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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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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Amount of sale 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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Amount of settlement 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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Amount of transfer of financial instrument classified as an asset into level 3 of the fair value hierarchy.

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Amount of transfers of financial instrument classified as an asset out of level 3 of the fair value hierarchy.

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

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

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