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	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Interest and Dividend Income, Securities, Operating	$ 2,211	$ 1,711	$ 1,599
Interest and Fee Income, Loans and Leases	24,728	23,388	21,203
Other Interest and Dividend Income	237	123	89
Interest Expense, Deposits	(2,598)	(1,602)	(1,213)
Interest Expense, Secured Debt	(496)	(327)	(216)
Interest Expense, Unsecured Debt	(1,125)	(731)	(476)
Other	1,002	$ 542	$ 541
Amortization of basis adjustment	75
Foreign Currency Transaction Loss, before Tax	193
Non Interest Income Other
Derivative Instruments, Gain (Loss) [Line Items]
Realized gains on foreign exchange contracts reclassified from AOCI	191
Fair value hedges | Interest income - Investment securities
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Fair Value Hedges Recognized in Earnings	(22)
Fair value hedges | Interest income - Loans
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Fair Value Hedges Recognized in Earnings	0
Fair value hedges | Interest income - Other
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Fair Value Hedges Recognized in Earnings	0
Fair value hedges | Interest expense - Deposits
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Fair Value Hedges Recognized in Earnings	(84)
Fair value hedges | Interest expense - Securitized Debt Obligation
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Fair Value Hedges Recognized in Earnings	(76)
Fair value hedges | Interest expense - Senior and Subordinated Debt
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Fair Value Hedges Recognized in Earnings	(79)
Fair value hedges | Non Interest Income Other
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Fair Value Hedges Recognized in Earnings	0
Fair value hedges | Interest rate contracts | Interest income - Investment securities
Derivative Instruments, Gain (Loss) [Line Items]
Gain or loss on fair value hedges recognized in net interest income	(23)
Gains (losses) recognized in earnings on derivatives	34
Gains (losses) recognized in earnings on hedged items	(33)
Fair value hedges | Interest rate contracts | Interest income - Loans
Derivative Instruments, Gain (Loss) [Line Items]
Gain or loss on fair value hedges recognized in net interest income	0
Gains (losses) recognized in earnings on derivatives	0
Gains (losses) recognized in earnings on hedged items	0
Fair value hedges | Interest rate contracts | Interest income - Other
Derivative Instruments, Gain (Loss) [Line Items]
Gain or loss on fair value hedges recognized in net interest income	0
Gains (losses) recognized in earnings on derivatives	0
Gains (losses) recognized in earnings on hedged items	0
Fair value hedges | Interest rate contracts | Interest expense - Deposits
Derivative Instruments, Gain (Loss) [Line Items]
Gain or loss on fair value hedges recognized in net interest income	(76)
Gains (losses) recognized in earnings on derivatives	(60)
Gains (losses) recognized in earnings on hedged items	52
Fair value hedges | Interest rate contracts | Interest expense - Securitized Debt Obligation
Derivative Instruments, Gain (Loss) [Line Items]
Gain or loss on fair value hedges recognized in net interest income	(53)
Gains (losses) recognized in earnings on derivatives	(61)
Gains (losses) recognized in earnings on hedged items	38
Fair value hedges | Interest rate contracts | Interest expense - Senior and Subordinated Debt
Derivative Instruments, Gain (Loss) [Line Items]
Gain or loss on fair value hedges recognized in net interest income	2
Gains (losses) recognized in earnings on derivatives	(212)
Gains (losses) recognized in earnings on hedged items	131
Fair value hedges | Interest rate contracts | Non Interest Income Other
Derivative Instruments, Gain (Loss) [Line Items]
Gain or loss on fair value hedges recognized in net interest income	0
Gains (losses) recognized in earnings on derivatives	0
Gains (losses) recognized in earnings on hedged items	0
Cash flow hedges | Interest income - Investment securities
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) On Cash Flow Hedges Recognized In Earnings	(9)
Cash flow hedges | Interest income - Loans
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) On Cash Flow Hedges Recognized In Earnings	(82)
Cash flow hedges | Interest income - Other
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) On Cash Flow Hedges Recognized In Earnings	47
Cash flow hedges | Interest expense - Deposits
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) On Cash Flow Hedges Recognized In Earnings	0
Cash flow hedges | Interest expense - Securitized Debt Obligation
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) On Cash Flow Hedges Recognized In Earnings	0
Cash flow hedges | Interest expense - Senior and Subordinated Debt
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) On Cash Flow Hedges Recognized In Earnings	0
Cash flow hedges | Non Interest Income Other
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) On Cash Flow Hedges Recognized In Earnings	(2)
Cash flow hedges | Interest rate contracts | Interest income - Investment securities
Derivative Instruments, Gain (Loss) [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	(9)
Cash flow hedges | Interest rate contracts | Interest income - Loans
Derivative Instruments, Gain (Loss) [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	(82)
Cash flow hedges | Interest rate contracts | Interest income - Other
Derivative Instruments, Gain (Loss) [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	0
Cash flow hedges | Interest rate contracts | Interest expense - Deposits
Derivative Instruments, Gain (Loss) [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	0
Cash flow hedges | Interest rate contracts | Interest expense - Securitized Debt Obligation
Derivative Instruments, Gain (Loss) [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	0
Cash flow hedges | Interest rate contracts | Interest expense - Senior and Subordinated Debt
Derivative Instruments, Gain (Loss) [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	0
Cash flow hedges | Interest rate contracts | Non Interest Income Other
Derivative Instruments, Gain (Loss) [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	0
Cash flow hedges | Foreign exchange contracts | Interest income - Investment securities
Derivative Instruments, Gain (Loss) [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	0
Cash flow hedges | Foreign exchange contracts | Interest income - Loans
Derivative Instruments, Gain (Loss) [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	0
Cash flow hedges | Foreign exchange contracts | Interest income - Other
Derivative Instruments, Gain (Loss) [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	47
Cash flow hedges | Foreign exchange contracts | Interest expense - Deposits
Derivative Instruments, Gain (Loss) [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	0
Cash flow hedges | Foreign exchange contracts | Interest expense - Securitized Debt Obligation
Derivative Instruments, Gain (Loss) [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	0
Cash flow hedges | Foreign exchange contracts | Interest expense - Senior and Subordinated Debt
Derivative Instruments, Gain (Loss) [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	0
Cash flow hedges | Foreign exchange contracts | Non Interest Income Other
Derivative Instruments, Gain (Loss) [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	$ (2)