Derivative Financial Instruments - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Derivative Liability, Fair Value, Gross Liability	$ 2,716	$ 4,442
Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net	178
Derivative, Notional Amount	233,052	249,705
Derivative Asset, Fair Value, Gross Asset	2,631	3,904
Netted counterparty balance [Member]
Fair Value, Concentration of Risk, Derivative Instruments, Assets	541	541
Derivative Asset, Fair Value of Collateral	350	399
Netted counterparty balance gains [Member]
Fair Value, Concentration of Risk, Derivative Instruments, Assets	891	940
Derivative liability positions containing provisions conditioned on downgrades [Member]
Derivative Liability, Fair Value, Gross Liability	589	1,100
Additional Termination Event [Member]
Derivative Liability, Fair Value, Gross Liability	1
Additional Termination Event [Member] \| Maximum [Member]
Derivative Liability, Fair Value, Gross Liability	10
Credit Support Annex [Member]
Derivative Liability, Fair Value, Gross Liability	580
Collateral Already Posted, Aggregate Fair Value	536
Credit Support Annex [Member] \| Moody's, Baa2 Rating [Member]
Additional Collateral, Aggregate Fair Value	1
Credit Support Annex [Member] \| Moody's, Baa3 Rating [Member]
Additional Collateral, Aggregate Fair Value	6
Credit Support Annex [Member] \| Moody's, Ba1 Rating [Member]
Additional Collateral, Aggregate Fair Value	10
Credit Default Swap, Buying Protection [Member]
Derivative, Notional Amount		5
Total Return Swap [Member]
Derivative Liability, Fair Value, Gross Liability	94	13
Collateral Already Posted, Aggregate Fair Value	601	368
Derivative, Notional Amount	2,000	1,700
Derivative Asset, Fair Value, Gross Asset	$ 97	$ 15
Financial Guarantee [Member]
Derivative, Average Remaining Maturity	5 years 10 months 24 days	5 years 6 months
Credit Derivative, Maximum Exposure, Undiscounted	$ 217	$ 55
Financial Guarantee [Member] \| Minimum [Member]
Derivative, Remaining Maturity	1 year	1 year
Financial Guarantee [Member] \| Maximum [Member]
Derivative, Remaining Maturity	10 years	9 years
Interest Rate Contract [Member] \| Cash Flow Hedging [Member]
Derivative, Average Remaining Maturity	2 years 6 months	3 years 7 months 6 days
Interest Rate Contract [Member] \| Minimum [Member] \| Cash Flow Hedging [Member]
Derivative, Remaining Maturity	1 year	1 year
Interest Rate Contract [Member] \| Maximum [Member] \| Cash Flow Hedging [Member]
Derivative, Remaining Maturity	5 years	5 years
Interest Income [Member] \| Loans Held-For-Investment [Member] \| Interest Rate Contract [Member] \| Cash Flow Hedging [Member]
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, before Tax	$ (161)	$ (54)	$ (145)

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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The aggregate fair value of additional assets that would be required to be posted as collateral for derivative instruments with credit-risk-related contingent features if the credit-risk-related contingent features were triggered at the end of the reporting period.

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The aggregate fair value of assets that are already posted, at the end of the reporting period, as collateral for derivative instruments with credit-risk-related contingent features.

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Maximum potential amount of future undiscounted payments that could be required under the credit derivative, before reduction for potential recoveries under recourse or collateralization provisions.

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Fair value of securities received as collateral against derivative assets.

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Average remaining period until maturity of the derivative contract, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

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Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

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Period remaining until the derivative contract matures, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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This item represents disclosure of all significant concentrations of credit risk or market risk arising from the subject financial instrument (as defined), whether from an individual counterparty or groups of counterparties.

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The estimated net amount of unrealized gains or losses on interest rate cash flow hedges as of the balance sheet date expected to be reclassified to earnings within the next twelve months.

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Amount before tax of increase (decrease) in accumulated gain (loss) from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's increase (decrease) in deferred hedging gain (loss).

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