Fair Value Measurements - Fair Values of Assets and Liabilities (Significant Unobservable Level 3 Inputs Recurring Basis) (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative assets	$ 3,499		$ 1,655
Derivative liabilities	1,294		$ 741
Residential mortgage loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Loans measured at FV	$ 185	$ 192
Residential mortgage loans | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Interest rate risk factor	(7.40%)	(9.50%)
Credit risk factor	0.00%	0.00%
Residential mortgage loans | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Interest rate risk factor	11.60%	5.30%
Credit risk factor	26.40%	34.50%
Residential mortgage loans | Weighted-Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Interest rate risk factor	0.70%	(0.20%)
Credit risk factor	0.40%	0.60%
Servicing rights
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Servicing rights	$ 676	$ 1,039
Servicing rights | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Prepayment speed	0.50%	1.00%
OAS Speed Assumption, OAS (bps)	536	441
Servicing rights | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Prepayment speed	99.60%	97.00%
OAS Speed Assumption, OAS (bps)	1,386	1,513
Servicing rights | Fixed | Weighted-Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Prepayment speed	20.10%	13.20%
OAS Speed Assumption, OAS (bps)	784	561
Servicing rights | Adjustable | Weighted-Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Prepayment speed	23.40%	23.50%
OAS Speed Assumption, OAS (bps)	934	909
IRLCs, net
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative assets	$ 91	$ 14
IRLCs, net | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Loan closing rates	7.20%	6.60%
IRLCs, net | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Loan closing rates	97.20%	96.60%
IRLCs, net | Weighted-Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Loan closing rates	65.70%	78.40%
Swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative liabilities	$ (183)	$ (151)
Swap | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Timing of the resolution of the Covered Litigation	Sep. 30, 2022	Jun. 30, 2021
Swap | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Timing of the resolution of the Covered Litigation	Jun. 30, 2024	Dec. 31, 2023
Swap | Weighted-Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Timing of the resolution of the Covered Litigation	Mar. 31, 2023	Mar. 31, 2022