Fair Value Measurements (Fair Values of Assets and Liabilities (Significant Unobservable Level 3 Inputs Nonrecurring Basis)) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Commercial Loans Held For Sale | Commercial
Quantitative Information About Level 3 Fair Value Measurements
Fair value measurements nonrecurring assets	$ 5	$ 1
Commercial and Industrial Loans | Commercial
Quantitative Information About Level 3 Fair Value Measurements
Fair value measurements nonrecurring assets	277	318
Commercial Mortgage Loans | Commercial
Quantitative Information About Level 3 Fair Value Measurements
Fair value measurements nonrecurring assets	4	25
Commercial Leases | Commercial
Quantitative Information About Level 3 Fair Value Measurements
Fair value measurements nonrecurring assets	2	2
OREO Property
Quantitative Information About Level 3 Fair Value Measurements
Fair value measurements nonrecurring assets	17	19
Bank premises and equipment
Quantitative Information About Level 3 Fair Value Measurements
Fair value measurements nonrecurring assets	4	15
Operating lease equipment
Quantitative Information About Level 3 Fair Value Measurements
Fair value measurements nonrecurring assets	12	$ 55
Private Equity Investments
Quantitative Information About Level 3 Fair Value Measurements
Comparable company analysis, fair value	4
Liquidity discount, fair value	$ 29
Minimum | Private Equity Investments
Quantitative Information About Level 3 Fair Value Measurements
Liquidity discount	0.00%
Maximum | Private Equity Investments
Quantitative Information About Level 3 Fair Value Measurements
Liquidity discount	43.00%
Weighted average | Commercial Loans Held For Sale
Quantitative Information About Level 3 Fair Value Measurements
Cost to sell	10.00%	10.00%
Weighted average | Private Equity Investments
Quantitative Information About Level 3 Fair Value Measurements
Liquidity discount	10.50%