Fair Value Measurements (Fair Value Measurements - Additional Information) (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Net fair value of the interest rate lock commitments	$ 11
Change in FV of IRLCs, due to 10% adverse changes in the assumed loan closing rates	1
Change in FV of IRLCs, due to 20% adverse changes in the assumed loan closing rates	2
Commercial aggregate borrower relationship subject to individual review for impairment	1
Operating lease equipment impairment	0	$ (2)
OTTI	0	0
Change in FV of IRLCs, due to 10% favorable changes in the assumed loan closing rates	1
Change in FV of IRLCs, due to 20% favorable changes in the assumed loan closing rates	2
Change In Fair Value of IRLC Due To Rate Increase 25 Bp	4
Change In Fair Value of IRLC Due To Rate Increase 50 Bp	10
Change In Fair Value of IRLC Due To Rate Decrease 25 Bp	4
Change In Fair Value of IRLC Due To Rate Decrease 50 Bp	7
Private Equity Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
OTTI		6
Private equity, observable price change adjustment	5	35
Private equity, impairment	3	10
Private equity, cumulative impairment	15
Private equity, cumulative observable price change	53
Transfer \| Other Real Estate Owned
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value adjustment	1	1
Existing \| Other Real Estate Owned
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value adjustment	1	2
Residential Mortgage Loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value gains or losses	23	$ 12
FVO valuation adjustments related to instrument-specific credit risk	$ 1		$ 1

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