Fair Value Measurements - Fair Values of Assets and Liabilities (Significant Unobservable Level 3 Inputs Recurring Basis) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative assets	$ 3,137		$ 1,655
Derivative liabilities	1,118		$ 741
Residential mortgage loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Loans measured at FV	$ 174	$ 184
Residential mortgage loans | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Interest rate risk factor	(8.60%)	(6.80%)
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	11.00%	6.90%
Credit risk factor	26.00%	31.80%
Residential mortgage loans | Weighted-Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Interest rate risk factor	1.10%	(0.20%)
Credit risk factor	0.40%	0.50%
Servicing rights
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Servicing rights	$ 660	$ 910
Servicing rights | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Prepayment speed	0.50%	0.50%
OAS Speed Assumption, OAS (bps)	536	484
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)	1,537	1,513
Servicing rights | Fixed | Weighted-Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Prepayment speed	18.20%	15.40%
OAS Speed Assumption, OAS (bps)	918	619
Servicing rights | Adjustable | Weighted-Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Prepayment speed	21.20%	23.40%
OAS Speed Assumption, OAS (bps)	938	914
IRLCs, net
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative assets	$ 85	$ 24
IRLCs, net | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Loan closing rates	7.20%	5.70%
IRLCs, net | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Loan closing rates	97.20%	96.70%
IRLCs, net | Weighted-Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Loan closing rates	61.40%	76.90%
Swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative liabilities	$ (188)	$ (146)
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