Fair Value Measurements (Fair Value Measurements - Additional Information) (Detail) - USD ($)	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Net fair value of the interest rate lock commitments	$ 18,000,000
Change in fair value of interest rate lock commitments, due to 10% adverse changes in the assumed loan closing rates	2,000,000
Change in fair value of interest rate lock commitments, due to 20% adverse changes in the assumed loan closing rates	4,000,000
Commercial aggregate borrower relationship subject to individual review for impairment	1,000,000
OTTI	1,000,000	$ 0	$ 54,000,000
Private equity, observable price change adjustment	13,000,000	64,000,000
Private equity, impairment	5,000,000	12,000,000
Private equity, cumulative impairment	17,000,000
Private equity, cumulative observable price change	47,000,000
Fair value changes included in earnings for instruments for which the fair value option was elected	37,000,000	20,000,000
Change in fair value of interest rate lock commitments, due to 10% favorable changes in the assumed loan closing rates	2,000,000
Change in fair value of interest rate lock commitments, due to 20% favorable changes in the assumed loan closing rates	4,000,000
Change in the fair value of the interest rate lock commitments, due to increase in current interest rates of 25 bp	13,000,000
Change in the fair value of the interest rate lock commitments, due to increase in current interest rates of 50 bp	28,000,000
Change in the fair value of the interest rate lock commitments, due to decrease in current interest rates of 25 bp	12,000,000
Change in the fair value of the interest rate lock commitments, due to decrease in current interest rates of 50 bp	22,000,000
Residential Mortgage Loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
FVO valuation adjustments related to instrument-specific credit risk	1,000,000	1,000,000
Other Real Estate Owned
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value adjustment	3,000,000	3,000,000
Other Real Estate Owned \| Transfer
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value gains or losses	3,000,000	4,000,000
Private equity investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
OTTI	$ 0	$ 10,000,000

Commercial Aggregate Borrower Relationship.

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Sensitivity analysis of decrease in fair value of derivatives impact of fifty basis point increase in interest rate.

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Sensitivity analysis of decrease in fair value of derivatives impact of twenty five basis point increase in interest rate.

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Sensitivity analysis of increase in fair value of derivatives impact of fifty basis point decrease in interest rate.

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Sensitivity analysis of increase in fair value of derivatives impact of ten percent changes in assumed loan closing rates.

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Sensitivity analysis of increase in fair value of derivatives impact of twenty five basis point decrease in interest rate.

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Amount of addition (reduction) to the amount at which an asset could be incurred (settled) in a current transaction between willing parties.

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Fair values as of the balance sheet date of the net amount of all assets and liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments.

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Amount of loss from downward price adjustment on investment in equity security without readily determinable fair value.

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Amount of cumulative loss from downward price adjustment on investment in equity security without readily determinable fair value.

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Amount of gain from upward price adjustment on investment in equity security without readily determinable fair value.

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Amount of cumulative gain from upward price adjustment on investment in equity security without readily determinable fair value.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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For each line item in the statement of financial position, the amounts of gains and losses from fair value changes included in earnings.

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This item represents the estimated amount of gains or losses included in earnings during the period attributable to changes in instrument-specific credit risk arising from loans and other receivables held as assets.

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The amount by which the fair value of an investment is less than the amortized cost basis or carrying amount of that investment at the balance sheet date and the decline in fair value is deemed to be other than temporary, before considering whether or not such amount is recognized in earnings or other comprehensive income.

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Amount of gain (loss) related to nonoperating activities, classified as other.

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The hypothetical financial impact of a 10 percent adverse change of the specified assumption on the fair value of transferor's interests in transferred financial assets (including any servicing assets or servicing liabilities) as of the balance sheet date.

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The hypothetical financial impact of a 20 percent adverse change of the specified assumption on the fair value of transferor's interests in transferred financial assets (including any servicing assets or servicing liabilities) as of the balance sheet date.

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