Fair Value Measurements (Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets	$ 173	$ 404
Fair Value Measured On Nonrecurring Basis Gains Losses	41	35
Commercial Loans Held-for-Sale | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets	0	5
Fair Value Measured On Nonrecurring Basis Gains Losses	0	1
Commercial and Industrial Loans | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets	109	277
Fair Value Measured On Nonrecurring Basis Gains Losses	20	44
Commercial Mortgage Loans | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets	9	4
Fair Value Measured On Nonrecurring Basis Gains Losses	0	(6)
Lease pool entities | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets	13	2
Fair Value Measured On Nonrecurring Basis Gains Losses	1	2
Other Real Estate Owned
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets	12	17
Fair Value Measured On Nonrecurring Basis Gains Losses	2	3
Bank premises and equipment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets	22	4
Fair Value Measured On Nonrecurring Basis Gains Losses	20	8
Operating lease equipment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets	0	12
Fair Value Measured On Nonrecurring Basis Gains Losses	0	2
Private Equity Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets	8	83
Fair Value Measured On Nonrecurring Basis Gains Losses	(2)	(19)
Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets	172	354
Fair Value, Inputs, Level 3 | Commercial Loans Held-for-Sale | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets	0	5
Fair Value, Inputs, Level 3 | Commercial and Industrial Loans | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets	109	277
Fair Value, Inputs, Level 3 | Commercial Mortgage Loans | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets	9	4
Fair Value, Inputs, Level 3 | Lease pool entities | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets	13	2
Fair Value, Inputs, Level 3 | Other Real Estate Owned
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets	12	17
Fair Value, Inputs, Level 3 | Bank premises and equipment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets	22	4
Fair Value, Inputs, Level 3 | Operating lease equipment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets	0	12
Fair Value, Inputs, Level 3 | Private Equity Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets	7	33
Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets	1	50
Fair Value, Inputs, Level 2 | Private Equity Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets	$ 1	$ 50