Derivative Financial Instruments - Net Gains (Losses) Recorded in the Condensed Consolidated Statements of Income Relating to Free-Standing Derivative Instruments Used for Risk Management and Other Business Purposes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Derivative Instruments, Gain (Loss)
Net gains (losses) recorded in earnings	$ 307	$ 221	$ (21)
Interest Rate Contract | Mortgage banking net revenue | Forward contracts | Residential mortgages held for sale
Derivative Instruments, Gain (Loss)
Net gains (losses) recorded in earnings	(12)	4	(8)
Interest Rate Contract | Mortgage banking net revenue | Servicing rights
Derivative Instruments, Gain (Loss)
Net gains (losses) recorded in earnings	307	221	(21)
Foreign Exchange Contract | Other noninterest income
Derivative Instruments, Gain (Loss)
Net gains (losses) recorded in earnings	(3)	(7)	10
Equity contracts | Other noninterest income | Swap
Derivative Instruments, Gain (Loss)
Net gains (losses) recorded in earnings	$ (103)	$ (107)	$ (59)