Derivative Instruments and Hedging Activities - Net Gains (Losses) Recognized in Earnings Related to Derivatives in Fair Value Hedging and Cash Flow Hedging (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Interest and dividend income, securities	$ 583	$ 593	$ 1,867	$ 1,584
Interest and fee income, loans	6,429	6,247	19,180	18,370
Interest and dividend income, other	63	55	196	174
Deposits	(901)	(681)	(2,588)	(1,842)
Securitized debt obligations	(123)	(127)	(405)	(358)
Senior and subordinated notes	(299)	(288)	(923)	(828)
Non-interest income	144	248	492	884
Amortization of basis adjustment	60	19	177	25
Non interest income - Other
Derivative Instruments, Gain (Loss) [Line Items]
Realized gains on foreign exchange contracts reclassified from AOCI	71	142	224	34
Fair value hedges | Interest income - Investment securities
Derivative Instruments, Gain (Loss) [Line Items]
Net expense recognized on fair value hedges	(2)	(7)	(3)	(21)
Fair value hedges | Interest income - Loans
Derivative Instruments, Gain (Loss) [Line Items]
Net expense recognized on fair value hedges	0	0	0	0
Fair value hedges | Interest income - Other
Derivative Instruments, Gain (Loss) [Line Items]
Net expense recognized on fair value hedges	0	0	0	0
Fair value hedges | Interest expense - Deposits
Derivative Instruments, Gain (Loss) [Line Items]
Net expense recognized on fair value hedges	(26)	(23)	(89)	(56)
Fair value hedges | Interest expense - Securitized Debt Obligation
Derivative Instruments, Gain (Loss) [Line Items]
Net expense recognized on fair value hedges	(21)	(20)	(80)	(48)
Fair value hedges | Interest expense - Senior and Subordinated Debt
Derivative Instruments, Gain (Loss) [Line Items]
Net expense recognized on fair value hedges	(49)	(20)	(149)	(43)
Fair value hedges | Non interest income - Other
Derivative Instruments, Gain (Loss) [Line Items]
Net expense recognized on fair value hedges	(2)	0	(1)	0
Fair value hedges | Interest rate contracts | Interest income - Investment securities
Derivative Instruments, Gain (Loss) [Line Items]
Interest recognized on derivatives	(3)	(5)	(2)	(22)
Gains (losses) recognized on derivatives	(80)	77	(366)	260
Gains (losses) recognized on hedged items	81	(79)	365	(259)
Excluded component of fair value hedges	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
Excluded component of fair value hedges	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
Excluded component of fair value hedges	0		0
Fair value hedges | Interest rate contracts | Interest expense - Deposits
Derivative Instruments, Gain (Loss) [Line Items]
Interest recognized on derivatives	(26)	(25)	(95)	(48)
Gains (losses) recognized on derivatives	46	(14)	295	(211)
Gains (losses) recognized on hedged items	(46)	16	(289)	203
Excluded component of fair value hedges	0		0
Fair value hedges | Interest rate contracts | Interest expense - Securitized Debt Obligation
Derivative Instruments, Gain (Loss) [Line Items]
Interest recognized on derivatives	(5)	(21)	(17)	(44)
Gains (losses) recognized on derivatives	(10)	(4)	102	(122)
Gains (losses) recognized on hedged items	(6)	5	(165)	118
Excluded component of fair value hedges	0		0
Fair value hedges | Interest rate contracts | Interest expense - Senior and Subordinated Debt
Derivative Instruments, Gain (Loss) [Line Items]
Interest recognized on derivatives	(3)	(8)	(24)	6
Gains (losses) recognized on derivatives	216	(148)	968	(659)
Gains (losses) recognized on hedged items	(261)	136	(1,092)	610
Excluded component of fair value hedges	(1)		(1)
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	(60)	0	(49)	0
Gains (losses) recognized on hedged items	58	0	48	0
Excluded component of fair value hedges	0		0
Cash flow hedges | Interest income - Investment securities
Derivative Instruments, Gain (Loss) [Line Items]
Net income (expense) recognized on cash flow hedges	(1)	(5)	(8)	(9)
Cash flow hedges | Interest income - Loans
Derivative Instruments, Gain (Loss) [Line Items]
Net income (expense) recognized on cash flow hedges	(43)	(31)	(158)	(40)
Cash flow hedges | Interest income - Other
Derivative Instruments, Gain (Loss) [Line Items]
Net income (expense) recognized on cash flow hedges	12	14	37	33
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	1	0	0	(1)
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	(1)	(5)	(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	(43)	(31)	(158)	(40)
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	12	14	37	33
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	$ 1	$ 0	$ 0	$ (1)