Fair Value Measurements (Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	$ 260	$ 249
Fair Value Measured On Nonrecurring Basis Gains (Losses)	(130)	(67)
Commercial loans held for sale | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements		16
Fair Value Measured On Nonrecurring Basis Gains (Losses)		(3)
Commercial and Industrial Loans | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	169	93
Fair Value Measured On Nonrecurring Basis Gains (Losses)	(96)	(41)
Commercial Mortgage Loans | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	12	2
Fair Value Measured On Nonrecurring Basis Gains (Losses)	0	7
Commercial Leases | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	20	14
Fair Value Measured On Nonrecurring Basis Gains (Losses)	(6)	(11)
Other Real Estate Owned
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	13	20
Fair Value Measured On Nonrecurring Basis Gains (Losses)	(6)	(7)
Bank premises and equipment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	27	32
Fair Value Measured On Nonrecurring Basis Gains (Losses)	(27)	(45)
Operating lease equipment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	6	0
Fair Value Measured On Nonrecurring Basis Gains (Losses)	(3)	(2)
Private equity investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	13	70
Fair Value Measured On Nonrecurring Basis Gains (Losses)	8	43
Other assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements		2
Fair Value Measured On Nonrecurring Basis Gains (Losses)		(8)
Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	249	182
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		16
Fair Value, Inputs, Level 3 | Commercial and Industrial Loans | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	169	93
Fair Value, Inputs, Level 3 | Commercial Mortgage Loans | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	12	2
Fair Value, Inputs, Level 3 | Commercial Leases | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	20	14
Fair Value, Inputs, Level 3 | Other Real Estate Owned
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	13	20
Fair Value, Inputs, Level 3 | Bank premises and equipment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	27	32
Fair Value, Inputs, Level 3 | Operating lease equipment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	6	0
Fair Value, Inputs, Level 3 | Private equity investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	2	3
Fair Value, Inputs, Level 3 | Other assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements		2
Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	11	67
Fair Value, Inputs, Level 2 | Commercial loans held for sale | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements		0
Fair Value, Inputs, Level 2 | Commercial and Industrial Loans | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	0	0
Fair Value, Inputs, Level 2 | Commercial Mortgage Loans | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	0	0
Fair Value, Inputs, Level 2 | Commercial Leases | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	0	0
Fair Value, Inputs, Level 2 | Other Real Estate Owned
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	0	0
Fair Value, Inputs, Level 2 | Bank premises and equipment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	0	0
Fair Value, Inputs, Level 2 | Operating lease equipment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	0	0
Fair Value, Inputs, Level 2 | Private equity investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	11	67
Fair Value, Inputs, Level 2 | Other assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements		0
Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	0	0
Fair Value, Inputs, Level 1 | Commercial loans held for sale | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements		0
Fair Value, Inputs, Level 1 | Commercial and Industrial Loans | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	0	0
Fair Value, Inputs, Level 1 | Commercial Mortgage Loans | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	0	0
Fair Value, Inputs, Level 1 | Commercial Leases | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	0	0
Fair Value, Inputs, Level 1 | Other Real Estate Owned
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	0	0
Fair Value, Inputs, Level 1 | Bank premises and equipment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	0	0
Fair Value, Inputs, Level 1 | Operating lease equipment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	0	0
Fair Value, Inputs, Level 1 | Private equity investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements	$ 0	0
Fair Value, Inputs, Level 1 | Other assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurements		$ 0