Fair Value Measurements - Fair Values of Recurring Assets and Liabilities With Significant Unobservable L3 Inputs (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage servicing rights	$ 910	$ 1,010
Derivative instruments	2,097		$ 1,114
Residential Mortgage
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans measured at fair value on a recurring basis	184	172
Interest Rate Lock Commitments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans measured at fair value on a recurring basis	24	7
Swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans measured at fair value on a recurring basis	$ (146)	$ (144)
Lower Limit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Prepayment speed	0.50%	0.50%
OAS spread (bps)	48400.00%	44900.00%
Lower Limit | Residential Mortgage
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate risk factor	(6.80%)	(12.70%)
Credit risk factor	0.00%	0.00%
Lower Limit | Interest Rate Lock Commitments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loan closing rates	5.70%	6.20%
Lower Limit | Swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Timing of the resolution of the covered litigation	Jun. 30, 2021	Jan. 31, 2021
Upper Limit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Prepayment speed	97.00%	97.00%
OAS spread (bps)	151300.00%	151300.00%
Upper Limit | Residential Mortgage
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate risk factor	0.069%	11.00%
Credit risk factor	31.80%	40.30%
Upper Limit | Interest Rate Lock Commitments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loan closing rates	96.70%	96.70%
Upper Limit | Swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Timing of the resolution of the covered litigation	Dec. 31, 2023	Nov. 30, 2023
Weighted average | Residential Mortgage
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate risk factor	(0.20%)	(0.60%)
Credit risk factor	0.005%	0.007%
Weighted average | Interest Rate Lock Commitments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loan closing rates	0.769%	0.766%
Weighted average | Swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Timing of the resolution of the covered litigation	Feb. 07, 2022	Sep. 06, 2021
Weighted average | Fixed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Prepayment speed	0.154%	0.091%
OAS spread (bps)	61900.00%	53300.00%
Weighted average | Adjustable
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Prepayment speed	0.234%	0.232%
OAS spread (bps)	91400.00%	84200.00%