Derivative Financial Instruments - Summary of Potential Effect of Offsetting Derivatives (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Derivative Asset [Abstract]
Gross Amounts of Recognized Assets/Liabilities	$ 4	$ 13
Gross Amounts Offset on our Condensed Consolidated Balance Sheets	0	0
Amounts of Assets/Liabilities Presented on our Condensed Consolidated Balance Sheets	4	13
Derivative Financial Instruments	(4)	(8)
Cash Collateral Received/ Pledged	0	0
Net Amount (Legal Offset)	0	5
Derivative Liability [Abstract]
Gross Amounts of Recognized Assets/Liabilities	(110)	(93)
Gross Amounts Offset on our Condensed Consolidated Balance Sheets	0	0
Amounts of Assets/Liabilities Presented on our Condensed Consolidated Balance Sheets	(110)	(93)
Derivative Financial Instruments	4	8
Cash Collateral Received/ Pledged	0	0
Net Amount (Legal Offset)	$ (106)	$ (85)

Fair value of liability associated with 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.

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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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