Derivative Instruments - Additional Information (Detail) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Derivative asset, Fair value	$ 567	$ 1,200
Derivative asset, Fair value	33	62
Derivative collateral obligation to return cash	508	998
Collateral securities as off-balance sheet	22	101
Derivative liability, Fair value	60	178
Derivative liability, Fair value	33	62
Derivative collateral right to reclaim cash	14	106
Initial Margin [Member]
Derivative asset, Fair value	$ 144	$ 114

Amount of obligation to return cash collateral under master netting arrangements offset against derivative assets.

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Fair value of 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, not subject to a master netting arrangement.

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Amount of obligation to return cash collateral under master netting arrangements that have not been offset against derivative assets.

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Amount of right to receive cash collateral under master netting arrangements that have not been offset against derivative liabilities.

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Fair value, after offset of derivative liability, of 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, before offset against an obligation to return collateral under a master netting arrangement. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

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Fair value, after offset of derivative asset, of 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, elected not to be and before offset against a right to receive collateral under a master netting arrangement. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

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