Derivative Instruments and Hedging Activities - Effects of Fair Value and Cash Flow Hedge Accounting (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Derivative Instruments, Gain (Loss) [Line Items]
Interest and dividend income, securities	$ 317	$ 443	$ 1,078	$ 1,455
Interest and fee income, loans	6,205	5,758	17,812	18,120
Interest and dividend income, other	16	14	48	67
Deposits	(228)	(476)	(734)	(1,818)
Securitized debt obligations	(29)	(43)	(89)	(198)
Senior and subordinated notes	(116)	(132)	(367)	(551)
Non-interest income	243	706	592	1,017
Amortization expense (benefit)	34	19	(10)	(34)
Non interest income - Other
Derivative Instruments, Gain (Loss) [Line Items]
Realized losses (gains) on foreign exchange contracts reclassified from AOCI	(83)	73	(245)	(20)
Fair value hedges | Interest income - Investment securities
Derivative Instruments, Gain (Loss) [Line Items]
Net income (expense) recognized on fair value hedges	(89)	(30)	(151)	(62)
Fair value hedges | Interest income - Loans
Derivative Instruments, Gain (Loss) [Line Items]
Net income (expense) recognized on fair value hedges	0	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	0
Fair value hedges | Interest expense - Deposits
Derivative Instruments, Gain (Loss) [Line Items]
Net income (expense) recognized on fair value hedges	30	45	100	70
Fair value hedges | Interest expense - Securitized Debt Obligation
Derivative Instruments, Gain (Loss) [Line Items]
Net income (expense) recognized on fair value hedges	27	33	79	62
Fair value hedges | Interest expense - Senior and Subordinated Debt
Derivative Instruments, Gain (Loss) [Line Items]
Net income (expense) recognized on fair value hedges	80	94	262	173
Fair value hedges | Non interest income - Other
Derivative Instruments, Gain (Loss) [Line Items]
Net income (expense) recognized on fair value hedges	0	0	0	0
Fair value hedges | Interest rate contracts | Interest income - Investment securities
Derivative Instruments, Gain (Loss) [Line Items]
Interest recognized on derivatives	(25)	(23)	(75)	(51)
Gains (losses) recognized on derivatives	19	24	130	(340)
Gains (losses) recognized on hedged items	(83)	(31)	(206)	329
Gain (Loss) from Components Excluded from Assessment of Fair Value Hedge Effectiveness, Net	0	0	0	0
Fair value hedges | Interest rate contracts | Interest income - Loans
Derivative Instruments, Gain (Loss) [Line Items]
Interest recognized on derivatives	0	0	0	0
Gains (losses) recognized on derivatives	0	0	0	0
Gains (losses) recognized on hedged items	0	0	0	0
Gain (Loss) from Components Excluded from Assessment of Fair Value Hedge Effectiveness, Net	0	0	0	0
Fair value hedges | Interest rate contracts | Interest income - Other
Derivative Instruments, Gain (Loss) [Line Items]
Interest recognized on derivatives	0	0	0	0
Gains (losses) recognized on derivatives	0	0	0	0
Gains (losses) recognized on hedged items	0	0	0	0
Gain (Loss) from Components Excluded from Assessment of Fair Value Hedge Effectiveness, Net	0	0	0	0
Fair value hedges | Interest rate contracts | Interest expense - Deposits
Derivative Instruments, Gain (Loss) [Line Items]
Interest recognized on derivatives	31	44	101	69
Gains (losses) recognized on derivatives	(28)	(47)	(117)	249
Gains (losses) recognized on hedged items	27	48	116	(248)
Gain (Loss) from Components Excluded from Assessment of Fair Value Hedge Effectiveness, Net	0	0	0	0
Fair value hedges | Interest rate contracts | Interest expense - Securitized Debt Obligation
Derivative Instruments, Gain (Loss) [Line Items]
Interest recognized on derivatives	30	40	93	92
Gains (losses) recognized on derivatives	(57)	(48)	(154)	221
Gains (losses) recognized on hedged items	54	41	140	(251)
Gain (Loss) from Components Excluded from Assessment of Fair Value Hedge Effectiveness, Net	0	0	0	0
Fair value hedges | Interest rate contracts | Interest expense - Senior and Subordinated Debt
Derivative Instruments, Gain (Loss) [Line Items]
Interest recognized on derivatives	50	56	168	166
Gains (losses) recognized on derivatives	(72)	(72)	(408)	1,057
Gains (losses) recognized on hedged items	103	111	504	(1,048)
Gain (Loss) from Components Excluded from Assessment of Fair Value Hedge Effectiveness, Net	(1)	(1)	(2)	(2)
Fair value hedges | Interest rate contracts | Non interest income - Other
Derivative Instruments, Gain (Loss) [Line Items]
Interest recognized on derivatives	0	0	0	0
Gains (losses) recognized on derivatives	(34)	61	(79)	64
Gains (losses) recognized on hedged items	34	(61)	79	(64)
Gain (Loss) from Components Excluded from Assessment of Fair Value Hedge Effectiveness, Net	0	0	0	0
Cash flow hedges | Interest income - Investment securities
Derivative Instruments, Gain (Loss) [Line Items]
Net income (expense) recognized on cash flow hedges	10	8	30	17
Cash flow hedges | Interest income - Loans
Derivative Instruments, Gain (Loss) [Line Items]
Net income (expense) recognized on cash flow hedges	240	171	700	330
Cash flow hedges | Interest income - Other
Derivative Instruments, Gain (Loss) [Line Items]
Net income (expense) recognized on cash flow hedges	0	1	1	10
Cash flow hedges | Interest expense - Deposits
Derivative Instruments, Gain (Loss) [Line Items]
Net income (expense) recognized on cash flow hedges	0	0	0	0
Cash flow hedges | Interest expense - Securitized Debt Obligation
Derivative Instruments, Gain (Loss) [Line Items]
Net income (expense) recognized on cash flow hedges	0	0	0	0
Cash flow hedges | Interest expense - Senior and Subordinated Debt
Derivative Instruments, Gain (Loss) [Line Items]
Net income (expense) recognized on cash flow hedges	0	0	0	0
Cash flow hedges | Non interest income - Other
Derivative Instruments, Gain (Loss) [Line Items]
Net income (expense) recognized on cash flow hedges	0	0	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	10	8	30	17
Cash flow hedges | Interest rate contracts | Interest income - Loans
Derivative Instruments, Gain (Loss) [Line Items]
Reclassification adjustment from AOCI on derivatives, net of tax	240	171	700	330
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	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	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	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	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	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	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	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	0	1	1	10
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	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	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	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	$ 0	$ 0	$ 1	$ (2)