Fair Value Measurements (Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets	$ 314	$ 484	$ 314	$ 484
Fair Value Measured On Nonrecurring Basis Gains Losses	(5)	(16)	(58)	(149)
Commercial Loans Held-for-Sale | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets	3	8	3	8
Fair Value Measured On Nonrecurring Basis Gains Losses	(1)	(1)	(2)	(33)
Commercial and Industrial Loans | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets	156	354	156	354
Fair Value Measured On Nonrecurring Basis Gains Losses	(16)	(10)	(46)	(68)
Commercial Mortgage Loans | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets	2	20	2	20
Fair Value Measured On Nonrecurring Basis Gains Losses	0	(1)	6	(12)
Commercial Leases | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets	14	1	14	1
Fair Value Measured On Nonrecurring Basis Gains Losses	1	0	(9)	(2)
Other Real Estate Owned
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets	21	20	21	20
Fair Value Measured On Nonrecurring Basis Gains Losses	(2)	(3)	(6)	(8)
Bank premises and equipment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets	36	25	36	25
Fair Value Measured On Nonrecurring Basis Gains Losses	0	(1)	(41)	(6)
Operating lease equipment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets	10	56	10	56
Fair Value Measured On Nonrecurring Basis Gains Losses	(1)	0	(4)	(20)
Private Equity Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets	72		72
Fair Value Measured On Nonrecurring Basis Gains Losses	14		44
Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets	245	484	245	484
Fair Value, Inputs, Level 3 | Commercial Loans Held-for-Sale | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets	3	8	3	8
Fair Value, Inputs, Level 3 | Commercial and Industrial Loans | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets	156	354	156	354
Fair Value, Inputs, Level 3 | Commercial Mortgage Loans | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets	2	20	2	20
Fair Value, Inputs, Level 3 | Commercial Leases | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets	14	1	14	1
Fair Value, Inputs, Level 3 | Other Real Estate Owned
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets	21	20	21	20
Fair Value, Inputs, Level 3 | Bank premises and equipment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets	36	25	36	25
Fair Value, Inputs, Level 3 | Operating lease equipment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets	10	56	10	56
Fair Value, Inputs, Level 3 | Private Equity Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets	3		3
Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets	69	0	69	0
Fair Value, Inputs, Level 2 | Commercial Loans Held-for-Sale | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets	0	0	0	0
Fair Value, Inputs, Level 2 | Commercial and Industrial Loans | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets	0	0	0	0
Fair Value, Inputs, Level 2 | Commercial Mortgage Loans | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets	0	0	0	0
Fair Value, Inputs, Level 2 | Commercial Leases | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets	0	0	0	0
Fair Value, Inputs, Level 2 | Other Real Estate Owned
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets	0	0	0	0
Fair Value, Inputs, Level 2 | Bank premises and equipment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets	0	0	0	0
Fair Value, Inputs, Level 2 | Operating lease equipment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets	0	$ 0	0	$ 0
Fair Value, Inputs, Level 2 | Private Equity Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets	$ 69		$ 69