Derivative Instruments - Schedule of Derivative Instruments Classified as Assets (Liabilities) (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Derivative [Line Items]
Derivative assets, current	$ 3	$ 14
Derivative assets, noncurrent	7	9
Derivative liabilities, current	6	2
Derivative liabilities, noncurrent	81	31
Designated Derivative Instruments \| Interest rate swaps
Derivative [Line Items]
Derivative assets, current	0	0
Derivative assets, noncurrent	0	3
Derivative liabilities, current	6	2
Derivative liabilities, noncurrent	81	25
Not Designated as Hedging Instrument \| Interest rate swaps
Derivative [Line Items]
Derivative assets, current		0
Derivative assets, noncurrent		0
Derivative liabilities, current		0
Derivative liabilities, noncurrent		4
Not Designated as Hedging Instrument \| Energy derivative
Derivative [Line Items]
Derivative assets, current		7
Derivative assets, noncurrent		0
Derivative liabilities, current		0
Derivative liabilities, noncurrent		0
Not Designated as Hedging Instrument \| Foreign currency forward contracts
Derivative [Line Items]
Derivative assets, current	3	6
Derivative assets, noncurrent	7	6
Derivative liabilities, current	0	0
Derivative liabilities, noncurrent	0	2
Not Designated as Hedging Instrument \| Congestion revenue rights
Derivative [Line Items]
Derivative assets, current	0	1
Derivative assets, noncurrent	0	0
Derivative liabilities, current	0	0
Derivative liabilities, noncurrent	0	$ 0
Derivative asset (less than $1 million for congestion revenue rights in September 30, 2019)	$ 1

Fair value, after the 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 not subject to a master netting arrangement and not elected to be offset.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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Fair value, after the 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, expected to be settled after one year or the normal operating cycle, if longer. Includes assets not subject to a master netting arrangement and not elected to be offset.

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