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Fair Value Measurements - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net fair value of the interest rate lock commitments	$ 24,000,000		$ 24,000,000
Change in FV of IRLCs, due to 10% adverse changes in the assumed loan closing rates	2,000,000		2,000,000
Change in FV of IRLCs, due to 20% adverse changes in the assumed loan closing rates	5,000,000		5,000,000
Commercial aggregate borrower relationship subject to individual review for impairment	1,000,000		1,000,000
Operating lease equipment impairment		$ 2,000,000		$ 4,000,000
OTTI	0	0	(1,000,000)	0
Private equity, observable price change adjustment	0	13,000,000	11,000,000	64,000,000
Private equity, impairment	0		5,000,000	11,000,000
Private equity, cumulative impairment	17,000,000		17,000,000
Private equity, cumulative observable price change	53,000,000		53,000,000
Fair value changes included in earnings for instruments for which the fair value option was elected			35,000,000	12,000,000
Change in FV of IRLCs, due to 10% favorable changes in the assumed loan closing rates	2,000,000		2,000,000
Change in FV of IRLCs, due to 20% favorable changes in the assumed loan closing rates	5,000,000		5,000,000
Change In Fair Value of IRLC Due To Rate Increase 25 Bp	11,000,000		11,000,000
Change In Fair Value of IRLC Due To Rate Increase 50 Bp	23,000,000		23,000,000
Change In Fair Value of IRLC Due To Rate Decrease 25 Bp	10,000,000		10,000,000
Change In Fair Value of IRLC Due To Rate Decrease 50 Bp	17,000,000		17,000,000
Other Real Estate Owned
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value adjustment	1,000,000	1,000,000	3,000,000	3,000,000
Private Equity Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
OTTI				10,000,000
Transfer \| Other Real Estate Owned
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value gains or losses	$ 1,000,000	$ 1,000,000	2,000,000	$ 3,000,000
Residential Mortgage Loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
FVO valuation adjustments related to instrument-specific credit risk			$ 1,000,000		$ 1,000,000