Fair Value Measurements (Fair Values of Assets and Liabilities (Significant Unobservable Level 3 Inputs Nonrecurring Basis)) (Detail) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Commercial Loans Held For Sale | Commercial
Quantitative Information About Level 3 Fair Value Measurements
Fair value measurements nonrecurring assets	$ 45	$ 20
Commercial and Industrial Loans | Commercial
Quantitative Information About Level 3 Fair Value Measurements
Fair value measurements nonrecurring assets	405	426
Commercial Mortgage Loans | Commercial
Quantitative Information About Level 3 Fair Value Measurements
Fair value measurements nonrecurring assets	26	67
Commercial construction loans | Commercial
Quantitative Information About Level 3 Fair Value Measurements
Fair value measurements nonrecurring assets		0
Commercial Leases | Commercial
Quantitative Information About Level 3 Fair Value Measurements
Fair value measurements nonrecurring assets	3	3
Servicing Rights
Quantitative Information About Level 3 Fair Value Measurements
Fair value measurements nonrecurring assets		621
OREO Property
Quantitative Information About Level 3 Fair Value Measurements
Fair value measurements nonrecurring assets	11	38
Bank premises and equipment
Quantitative Information About Level 3 Fair Value Measurements
Fair value measurements nonrecurring assets	16	20
Operating lease equipment
Quantitative Information About Level 3 Fair Value Measurements
Fair value measurements nonrecurring assets	$ 56	$ 38
Minimum | Residential mortgage loans
Quantitative Information About Level 3 Fair Value Measurements
Interest rate risk factor	(9.60%)	(5.20%)
Credit risk factor	0.00%	0.00%
Minimum | Servicing Rights
Quantitative Information About Level 3 Fair Value Measurements
Prepayment speed	1.20%	0.00%
OAS spread (bps)	4.30%	4.04%
Maximum | Residential mortgage loans
Quantitative Information About Level 3 Fair Value Measurements
Interest rate risk factor	15.00%	16.30%
Credit risk factor	46.20%	80.50%
Maximum | Servicing Rights
Quantitative Information About Level 3 Fair Value Measurements
Prepayment speed	100.00%	100.00%
OAS spread (bps)	15.15%	15.15%
Weighted average | Commercial Loans Held For Sale
Quantitative Information About Level 3 Fair Value Measurements
Cost to sell		10.00%
Weighted average | Residential mortgage loans
Quantitative Information About Level 3 Fair Value Measurements
Interest rate risk factor	2.90%	5.00%
Credit risk factor	1.00%	1.10%
Weighted average | Fixed | Servicing Rights
Quantitative Information About Level 3 Fair Value Measurements
Prepayment speed	11.50%	15.00%
OAS spread (bps)	5.30%	6.48%
Weighted average | Adjustable | Servicing Rights
Quantitative Information About Level 3 Fair Value Measurements
Prepayment speed	24.80%	26.90%
OAS spread (bps)	7.73%	7.62%