Fair Value Measurements (Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis) (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	$ 327	$ 562	$ 327	$ 562
Fair Value Measured On Nonrecurring Basis Gains Losses	(18)	(58)	(53)	(133)
Commercial Loans Held-for-Sale | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	4	45	4	45
Fair Value Measured On Nonrecurring Basis Gains Losses	0	(13)	(1)	(32)
Commercial and Industrial Loans | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	161	405	161	405
Fair Value Measured On Nonrecurring Basis Gains Losses	14	(32)	(30)	(58)
Commercial Mortgage Loans | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	3	26	3	26
Fair Value Measured On Nonrecurring Basis Gains Losses	1	(9)	6	(11)
Commercial Leases | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	14	3	14	3
Fair Value Measured On Nonrecurring Basis Gains Losses	(9)	(1)	(10)	(2)
Other Real Estate Owned
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	17	11	17	11
Fair Value Measured On Nonrecurring Basis Gains Losses	(1)	(1)	(4)	(5)
Bank premises and equipment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	37	16	37	16
Fair Value Measured On Nonrecurring Basis Gains Losses	(33)	(2)	(41)	(5)
Operating lease equipment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	10	56	10	56
Fair Value Measured On Nonrecurring Basis Gains Losses	(1)	0	(3)	(20)
Private Equity Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	81		81
Fair Value Measured On Nonrecurring Basis Gains Losses	11		30
Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	277	562	277	562
Fair Value, Inputs, Level 3 | Commercial Loans Held-for-Sale | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	4	45	4	45
Fair Value, Inputs, Level 3 | Commercial and Industrial Loans | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	161	405	161	405
Fair Value, Inputs, Level 3 | Commercial Mortgage Loans | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	3	26	3	26
Fair Value, Inputs, Level 3 | Commercial Leases | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	14	3	14	3
Fair Value, Inputs, Level 3 | Other Real Estate Owned
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	17	11	17	11
Fair Value, Inputs, Level 3 | Bank premises and equipment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	37	16	37	16
Fair Value, Inputs, Level 3 | Operating lease equipment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	10	$ 56	10	$ 56
Fair Value, Inputs, Level 3 | Private Equity Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	31		31
Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	50		50
Fair Value, Inputs, Level 2 | Private Equity Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	$ 50		$ 50