Fair Value Measurements (Fair Values of Assets and Liabilities (Significant Unobservable Level 3 Inputs Nonrecurring Basis)) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Commercial Loans Held For Sale | Commercial
Quantitative Information About Level 3 Fair Value Measurements
Fair value measurements nonrecurring assets	$ 1	$ 5
Commercial and Industrial Loans | Commercial
Quantitative Information About Level 3 Fair Value Measurements
Fair value measurements nonrecurring assets	327	412
Commercial Mortgage Loans | Commercial
Quantitative Information About Level 3 Fair Value Measurements
Fair value measurements nonrecurring assets	19	15
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	4
Residential mortgage loans
Quantitative Information About Level 3 Fair Value Measurements
Fair value measurements nonrecurring assets		3
Mortgage Servicing Rights
Quantitative Information About Level 3 Fair Value Measurements
Fair value measurements nonrecurring assets	744
OREO Property
Quantitative Information About Level 3 Fair Value Measurements
Fair value measurements nonrecurring assets	27	42
Bank premises and equipment
Quantitative Information About Level 3 Fair Value Measurements
Fair value measurements nonrecurring assets	24	28
Operating lease equipment
Quantitative Information About Level 3 Fair Value Measurements
Fair value measurements nonrecurring assets	60	37
Private equity investments
Quantitative Information About Level 3 Fair Value Measurements
Fair value measurements nonrecurring assets	8	$ 60
Affordable Housing Investments
Quantitative Information About Level 3 Fair Value Measurements
Fair value measurements nonrecurring assets	$ 1,178
Minimum | Residential mortgage loans
Quantitative Information About Level 3 Fair Value Measurements
Interest rate risk factor	(10.60%)	(11.50%)
Credit risk factor	0.00%	0.00%
Minimum | Mortgage Servicing Rights
Quantitative Information About Level 3 Fair Value Measurements
Prepayment speed	0.00%	0.70%
OAS spread (bps)	45000.00%	10000.00%
Minimum | Private equity investments
Quantitative Information About Level 3 Fair Value Measurements
Liquidity discount	2.50%	5.00%
Maximum | Residential mortgage loans
Quantitative Information About Level 3 Fair Value Measurements
Interest rate risk factor	14.50%	13.80%
Credit risk factor	52.10%	75.60%
Maximum | Mortgage Servicing Rights
Quantitative Information About Level 3 Fair Value Measurements
Prepayment speed	98.10%	100.00%
OAS spread (bps)	151500.00%	151500.00%
Maximum | Private equity investments
Quantitative Information About Level 3 Fair Value Measurements
Liquidity discount	15.00%	37.50%
Weighted-average | Commercial Loans Held For Sale | Commercial
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	3.10%	2.30%
Credit risk factor	1.40%	1.40%
Weighted-average | Private equity investments
Quantitative Information About Level 3 Fair Value Measurements
Liquidity discount	5.80%	12.80%
Weighted-average | Fixed | Mortgage Servicing Rights
Quantitative Information About Level 3 Fair Value Measurements
Prepayment speed	11.40%	10.20%
OAS spread (bps)	54900.00%	65400.00%
Weighted-average | Adjustable | Mortgage Servicing Rights
Quantitative Information About Level 3 Fair Value Measurements
Prepayment speed	24.60%	25.30%
OAS spread (bps)	78500.00%	73800.00%