Derivative Financial Instruments - Summary of Derivative Activity and Related Impact on Consolidated Statements of Income (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]
Unrealized gains (losses) on derivatives			$ (5)	$ 88
Interest rate risks | Derivatives designated as hedging instruments
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized gains (losses) on derivatives	$ 15	$ 16	46	34
Interest rate risks | Derivatives designated as hedging instruments | Reclassification out of Accumulated Other Comprehensive Income | Interest income - loans
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized gains (losses) on derivatives	16	16	47	34
Interest rate risks | Derivatives designated as hedging instruments | Change In Fair Value Of Interest Rate Swaps Hedging Investment Securities | Interest income - loans
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized gains (losses) on derivatives	5	0	18	0
Interest rate risks | Derivatives designated as hedging instruments | Change In Fair Value Of Hedged Investment Securities | Interest income - loans
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized gains (losses) on derivatives	(6)	0	(19)	0
Currency exchange risk | Derivatives not designated as hedging instruments
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized gains (losses) on derivatives	0	(2)	0	0
Currency exchange risk | Derivatives not designated as hedging instruments | Revaluations of internal foreign currency instruments, net | Other noninterest income
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized gains (losses) on derivatives	(14)	17	(35)	20
Currency exchange risk | Derivatives not designated as hedging instruments | Foreign exchange forward contracts, net | Other noninterest income
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized gains (losses) on derivatives	14	(19)	35	(20)
Other derivative instruments | Derivatives not designated as hedging instruments
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized gains (losses) on derivatives	(4)	2	1	(1)
Other derivative instruments | Derivatives not designated as hedging instruments | Other noninterest income
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized gains (losses) on derivatives	2	31	4	27
Other derivative instruments | Derivatives not designated as hedging instruments | Revaluations of internal foreign currency instruments, net | Other noninterest income
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized gains (losses) on derivatives	1	0	16	(3)
Other derivative instruments | Derivatives not designated as hedging instruments | Foreign exchange forward contracts, net | Other noninterest income
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized gains (losses) on derivatives	(5)	2	(15)	2
Equity warrant assets | Derivatives not designated as hedging instruments | Gains on equity warrant assets, net
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized gains (losses) on derivatives	$ 147	$ 54	$ 491	$ 94