Derivative Instruments and Hedging Activities - Effects of Fair Value and Cash Flow Hedge Accounting (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Interest and dividend income, securities	$ 1,877	$ 2,411	$ 2,211
Interest and fee income, loans	24,074	25,862	24,728
Interest and dividend income, other	82	240	237
Deposits	(2,165)	(3,420)	(2,598)
Securitized debt obligations	(232)	(523)	(496)
Senior and subordinated notes	(679)	(1,159)	(1,125)
Non-interest income	1,325	718	1,002
Amortization of basis adjustment	12	171	75
Non interest income - Other
Derivative Instruments, Gain (Loss) [Line Items]
Realized (losses) gains on foreign exchange contracts reclassified from AOCI	(57)	(341)	191
Fair value hedges \| Interest income - Investment securities
Derivative Instruments, Gain (Loss) [Line Items]
Net income (expense) recognized on fair value hedges	(92)	(12)	(22)
Fair value hedges \| Interest income - Loans
Derivative Instruments, Gain (Loss) [Line Items]
Net income (expense) recognized on fair value hedges	0	0	0
Fair value hedges \| Interest income - Other
Derivative Instruments, Gain (Loss) [Line Items]
Net income (expense) recognized on fair value hedges	0	0	0
Fair value hedges \| Interest expense - Deposits
Derivative Instruments, Gain (Loss) [Line Items]
Net income (expense) recognized on fair value hedges	109	(103)	(84)
Fair value hedges \| Interest expense - Securitized Debt Obligation
Derivative Instruments, Gain (Loss) [Line Items]
Net income (expense) recognized on fair value hedges	89	(92)	(76)
Fair value hedges \| Interest expense - Senior and Subordinated Debt
Derivative Instruments, Gain (Loss) [Line Items]
Net income (expense) recognized on fair value hedges	268	(105)	(79)
Fair value hedges \| Non interest income - Other
Derivative Instruments, Gain (Loss) [Line Items]
Net income (expense) recognized on fair value hedges	1	0	0
Fair value hedges \| Interest rate contracts \| Interest income - Investment securities
Derivative Instruments, Gain (Loss) [Line Items]
Interest recognized on derivatives	(76)	(12)	(23)
Gains (losses) recognized on derivatives	(306)	(278)	34
Gains (losses) recognized on hedged items	290	278	(33)
Gain (Loss) from Components Excluded from Assessment of Fair Value Hedge Effectiveness, Net	0	0
Fair value hedges \| Interest rate contracts \| Interest income - Loans
Derivative Instruments, Gain (Loss) [Line Items]
Interest recognized on derivatives	0	0	0
Gains (losses) recognized on derivatives	0	0	0
Gains (losses) recognized on hedged items	0	0	0
Gain (Loss) from Components Excluded from Assessment of Fair Value Hedge Effectiveness, Net	0	0
Fair value hedges \| Interest rate contracts \| Interest income - Other
Derivative Instruments, Gain (Loss) [Line Items]
Interest recognized on derivatives	0	0	0
Gains (losses) recognized on derivatives	0	0	0
Gains (losses) recognized on hedged items	0	0	0
Gain (Loss) from Components Excluded from Assessment of Fair Value Hedge Effectiveness, Net	0	0
Fair value hedges \| Interest rate contracts \| Interest expense - Deposits
Derivative Instruments, Gain (Loss) [Line Items]
Interest recognized on derivatives	108	(108)	(76)
Gains (losses) recognized on derivatives	204	263	(60)
Gains (losses) recognized on hedged items	(203)	(258)	52
Gain (Loss) from Components Excluded from Assessment of Fair Value Hedge Effectiveness, Net	0	0
Fair value hedges \| Interest rate contracts \| Interest expense - Securitized Debt Obligation
Derivative Instruments, Gain (Loss) [Line Items]
Interest recognized on derivatives	125	(14)	(53)
Gains (losses) recognized on derivatives	176	45	(61)
Gains (losses) recognized on hedged items	(212)	(123)	38
Gain (Loss) from Components Excluded from Assessment of Fair Value Hedge Effectiveness, Net	0	0
Fair value hedges \| Interest rate contracts \| Interest expense - Senior and Subordinated Debt
Derivative Instruments, Gain (Loss) [Line Items]
Interest recognized on derivatives	225	(6)	2
Gains (losses) recognized on derivatives	950	704	(212)
Gains (losses) recognized on hedged items	(904)	(801)	131
Gain (Loss) from Components Excluded from Assessment of Fair Value Hedge Effectiveness, Net	(3)	(2)
Fair value hedges \| Interest rate contracts \| Non interest income - Other
Derivative Instruments, Gain (Loss) [Line Items]
Interest recognized on derivatives	0	0	0
Gains (losses) recognized on derivatives	126	(9)	0
Gains (losses) recognized on hedged items	(125)	9	0
Gain (Loss) from Components Excluded from Assessment of Fair Value Hedge Effectiveness, Net	0	0
Cash flow hedges \| Interest income - Investment securities
Derivative Instruments, Gain (Loss) [Line Items]
Net income recognized on cash flow hedges	25	(8)	(9)
Cash flow hedges \| Interest income - Loans
Derivative Instruments, Gain (Loss) [Line Items]
Net income recognized on cash flow hedges	541	(163)	(82)
Cash flow hedges \| Interest income - Other
Derivative Instruments, Gain (Loss) [Line Items]
Net income recognized on cash flow hedges	10	44	47
Cash flow hedges \| Interest expense - Deposits
Derivative Instruments, Gain (Loss) [Line Items]
Net income recognized on cash flow hedges	0	0	0
Cash flow hedges \| Interest expense - Securitized Debt Obligation
Derivative Instruments, Gain (Loss) [Line Items]
Net income recognized on cash flow hedges	0	0	0
Cash flow hedges \| Interest expense - Senior and Subordinated Debt
Derivative Instruments, Gain (Loss) [Line Items]
Net income recognized on cash flow hedges	0	0	0
Cash flow hedges \| Non interest income - Other
Derivative Instruments, Gain (Loss) [Line Items]
Net income recognized on cash flow hedges	(1)	(1)	(2)
Cash flow hedges \| Interest rate contracts \| Interest income - Investment securities
Derivative Instruments, Gain (Loss) [Line Items]
Reclassification adjustment from AOCI on derivatives, net of tax	25	(8)	(9)
Cash flow hedges \| Interest rate contracts \| Interest income - Loans
Derivative Instruments, Gain (Loss) [Line Items]
Reclassification adjustment from AOCI on derivatives, net of tax	541	(163)	(82)
Cash flow hedges \| Interest rate contracts \| Interest income - Other
Derivative Instruments, Gain (Loss) [Line Items]
Reclassification adjustment from AOCI on derivatives, net of tax	0	0	0
Cash flow hedges \| Interest rate contracts \| Interest expense - Deposits
Derivative Instruments, Gain (Loss) [Line Items]
Reclassification adjustment from AOCI on derivatives, net of tax	0	0	0
Cash flow hedges \| Interest rate contracts \| Interest expense - Securitized Debt Obligation
Derivative Instruments, Gain (Loss) [Line Items]
Reclassification adjustment from AOCI on derivatives, net of tax	0	0	0
Cash flow hedges \| Interest rate contracts \| Interest expense - Senior and Subordinated Debt
Derivative Instruments, Gain (Loss) [Line Items]
Reclassification adjustment from AOCI on derivatives, net of tax	0	0	0
Cash flow hedges \| Interest rate contracts \| Non interest income - Other
Derivative Instruments, Gain (Loss) [Line Items]
Reclassification adjustment from AOCI on derivatives, net of tax	0	0	0
Cash flow hedges \| Foreign exchange contracts \| Interest income - Investment securities
Derivative Instruments, Gain (Loss) [Line Items]
Reclassification adjustment from AOCI on derivatives, net of tax	0	0	0
Cash flow hedges \| Foreign exchange contracts \| Interest income - Loans
Derivative Instruments, Gain (Loss) [Line Items]
Reclassification adjustment from AOCI on derivatives, net of tax	0	0	0
Cash flow hedges \| Foreign exchange contracts \| Interest income - Other
Derivative Instruments, Gain (Loss) [Line Items]
Reclassification adjustment from AOCI on derivatives, net of tax	10	44	47
Cash flow hedges \| Foreign exchange contracts \| Interest expense - Deposits
Derivative Instruments, Gain (Loss) [Line Items]
Reclassification adjustment from AOCI on derivatives, net of tax	0	0	0
Cash flow hedges \| Foreign exchange contracts \| Interest expense - Securitized Debt Obligation
Derivative Instruments, Gain (Loss) [Line Items]
Reclassification adjustment from AOCI on derivatives, net of tax	0	0	0
Cash flow hedges \| Foreign exchange contracts \| Interest expense - Senior and Subordinated Debt
Derivative Instruments, Gain (Loss) [Line Items]
Reclassification adjustment from AOCI on derivatives, net of tax	0	0	0
Cash flow hedges \| Foreign exchange contracts \| Non interest income - Other
Derivative Instruments, Gain (Loss) [Line Items]
Reclassification adjustment from AOCI on derivatives, net of tax	$ (1)	$ (1)	$ (2)

Amortization of basis adjustment

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Total amount of gain (loss) derived from cash flow hedges recognized in earnings in the period

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Gain or loss on fair value hedges recognized in net interest income

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Interest Expense, Secured Debt

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Realized Gains (Losses) on Foreign Exchange Contracts Reclassified from AOCI

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Amount of gain (loss) from the increase (decrease) in fair value of derivative and nonderivative instruments designated as fair value hedging instruments recognized in the income statement.

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Amount of the increase (decrease) in fair value of the hedged item in a fair value hedge recognized in the income statement.

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Net gain (loss) relating to components of the gain (loss) on the fair value hedging instrument excluded from the assessment of fair value hedge effectiveness. Recognized in earnings.

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Total amount of gain (loss) derived from fair value hedges recognized in earnings in the period.

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Amount of operating dividend and interest income, including amortization and accretion of premiums and discounts, on securities.

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The aggregate interest and fee income generated by: (1) loans the Entity has positive intent and ability to hold for the foreseeable future, or until maturity or payoff, including commercial and consumer loans, whether domestic or foreign, which may consist of: (a) industrial and agricultural; (b) real estate; and (c) real estate construction loans; (d) trade financing; (e) lease financing; (f) home equity lines-of-credit; (g) automobile and other vehicle loans; and (h) credit card and other revolving-type loans and (2) loans and leases held-for-sale which may include mortgage loans, direct financing, and sales-type leases.

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