Fair Value Measurements - Total Gains and Losses Included in Earning Attributable to Changes in Unrealized Gains and Losses Related to Level 3 Assets and Liabilities Still Held at Year End (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Gain and losses included in earnings	$ (269)	$ (338)	$ (57)
Mortgage banking net revenue
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Gain and losses included in earnings	(167)	(233)	0
Commercial banking revenue
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Gain and losses included in earnings	2	2	2
Other noninterest income
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Gain and losses included in earnings	$ (104)	$ (107)	$ (59)