Derivative Instruments - Offsetting Assets and Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Offsetting Derivative Assets
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	$ 2,515	$ 2,551
Gross amounts not offset on the consolidated balance sheets, financial instruments	(63)	(59)
Gross amounts not offset on the consolidated balance sheets, collateral received/pledged	(2,315)	(2,323)
Derivative Asset, Fair Value, Amount Offset Against Collateral	137	169
Off-balance sheet securities collateral	(128)	(221)
Net amount after securities collateral	9	(52)
Offsetting Derivative Liabilities
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	(124)	(134)
Gross amounts not offset on the consolidated balance sheets, financial instruments	63	59
Gross amounts not offset on the consolidated balance sheets, collateral received/pledged	67	63
Derivative Liability, Fair Value, Amount Offset Against Collateral	6	(12)
Off-balance sheet securities collateral	0	0
Net amount after securities collateral	$ 6	$ (12)

Fair value, after effects of master netting arrangements, deduction of assets not subject to a master netting arrangement and elected not to be offset, 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, offset against an obligation to return collateral.

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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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