Fair Value Measurements (Fair Values of Assets and Liabilities (Significant Unobservable Level 3 Inputs Recurring Basis)) (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Loans measured at fair value on a recurring basis	$ 1,010	$ 848
Fair value - Derivative Assets	984		$ 823
Residential Mortgage
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Loans measured at fair value on a recurring basis	172	140
Interest Rate Lock Commitments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Loans measured at fair value on a recurring basis	7	13
Swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Loans measured at fair value on a recurring basis	$ (144)	$ (136)
Lower Limit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Prepayment speed	0.50%	0.80%
OAS spread (bps)	4.49%	4.30%
Lower Limit | Residential Mortgage
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Interest rate risk factor	(12.70%)	(9.20%)
Credit risk factor	0.00%	0.00%
Lower Limit | Interest Rate Lock Commitments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Loan closing rates	6.20%	3.30%
Lower Limit | Swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Timing of the resolution of the covered litigation	Jan. 31, 2021	Dec. 31, 2020
Upper Limit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Prepayment speed	97.00%	98.00%
OAS spread (bps)	15.13%	15.15%
Upper Limit | Residential Mortgage
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Interest rate risk factor	11.00%	14.90%
Credit risk factor	40.30%	46.20%
Upper Limit | Interest Rate Lock Commitments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Loan closing rates	96.70%	96.50%
Upper Limit | Swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Timing of the resolution of the covered litigation	Nov. 30, 2023	Dec. 31, 2023
Weighted average | Residential Mortgage
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Interest rate risk factor	(0.60%)	3.20%
Credit risk factor	0.70%	1.00%
Weighted average | Interest Rate Lock Commitments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Loan closing rates	76.60%	72.80%
Weighted average | Swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Timing of the resolution of the covered litigation	Sep. 06, 2021	Aug. 15, 2021
Weighted average | Fixed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Prepayment speed	9.10%	11.80%
OAS spread (bps)	5.33%	5.02%
Weighted average | Adjustable
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Prepayment speed	23.20%	25.20%
OAS spread (bps)	8.42%	7.84%