Derivative Financial Instruments and Hedging Activities - Fair Value (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Derivatives, Fair Value [Line Items]
Notional	$ 157,689	$ 163,446
Fair Value of Assets	1,691	1,809
Fair Value of Liabilities	2,815	2,563
Fair value of assets (liabilities) available for offset	1,100	1,200
Other Liabilities
Derivatives, Fair Value [Line Items]
Collateral held for netting against asset positions	447	457
Other Assets
Derivatives, Fair Value [Line Items]
Collateral available for netting against liability positions	1,200	1,200
Interest rate swaps | Fair value hedges | Level 2 | Derivatives designated as hedges
Derivatives, Fair Value [Line Items]
Notional	21,991	18,379
Fair Value of Assets	9	75
Fair Value of Liabilities	352	238
Interest rate swaps | Cash flow hedges | Level 2 | Derivatives designated as hedges
Derivatives, Fair Value [Line Items]
Notional	2,447	2,381
Fair Value of Assets	16	17
Fair Value of Liabilities	10	16
Foreign currency swaps | Cash flow hedges | Level 2 | Derivatives designated as hedges
Derivatives, Fair Value [Line Items]
Notional	9,208	8,003
Fair Value of Assets	88	144
Fair Value of Liabilities	428	311
Interest rate contracts | Level 2 | Derivatives not designated as hedges
Derivatives, Fair Value [Line Items]
Notional	123,103	134,683
Fair Value of Assets	1,576	1,573
Fair Value of Liabilities	2,024	1,997
Foreign currency contracts | Level 2 | Derivatives not designated as hedges
Derivatives, Fair Value [Line Items]
Notional	940	0
Fair Value of Assets	2	0
Fair Value of Liabilities	$ 0	$ 0