Fair Value Measurements - Fair Values of Assets and Liabilities (Significant Unobservable Level 3 Inputs Recurring Basis) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative assets	$ 2,478		$ 2,862
Derivative liabilities	(1,226)		(1,072)
Servicing rights
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Servicing rights	$ 784	$ 685
Servicing rights | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Prepayment speed	0.40%	0.50%
OAS Speed Assumption, OAS (bps)	536	536
Servicing rights | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Prepayment speed	99.90%	97.00%
OAS Speed Assumption, OAS (bps)	1,587	1,513
Servicing rights | Fixed | Weighted-Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Prepayment speed	13.00%	19.50%
OAS Speed Assumption, OAS (bps)	645	926
Servicing rights | Adjustable | Weighted-Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Prepayment speed	21.40%	23.80%
OAS Speed Assumption, OAS (bps)	968	932
IRLCs, net
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative assets	$ 38	$ 69
IRLCs, net | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Loan closing rates	7.20%	7.30%
IRLCs, net | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Loan closing rates	97.20%	97.20%
IRLCs, net | Weighted-Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Loan closing rates	75.90%	70.10%
Swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative liabilities	$ (195)	$ (171)
Swap | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Timing of the resolution of the Covered Litigation	Dec. 31, 2022	Jun. 30, 2022
Swap | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Timing of the resolution of the Covered Litigation	Dec. 31, 2024	Mar. 31, 2024
Swap | Weighted-Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Timing of the resolution of the Covered Litigation	Sep. 30, 2023	Dec. 31, 2022
Residential Mortgage
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Loans measured at FV	$ 153	$ 185	$ 161
Residential Mortgage | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Interest rate risk factor	(9.30%)	(2.10%)
Credit risk factor	0.00%	0.00%
Residential Mortgage | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Interest rate risk factor	7.80%	13.10%
Credit risk factor	25.60%	40.60%
Residential Mortgage | Weighted-Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Interest rate risk factor	0.80%	2.20%
Credit risk factor	0.40%	0.70%