Fair Value Measurements of Assets and Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Long-term Debt	$ 2,473	$ 2,342
Project Debt	134	152
Estimate of Fair Value Measurement [Member]
Assets, Fair Value Disclosure	2	2
Financial and Nonfinancial Liabilities, Fair Value Disclosure	3	13
Long-term Debt	2,546	2,245
Project Debt	140	154
Reported Value Measurement [Member]
Long-term Debt	2,473	2,342
Project Debt	134	152
Fair Value, Inputs, Level 1 [Member] \| Mutual And Bond Funds [Member] \| Estimate of Fair Value Measurement [Member]
Investments, Fair Value Disclosure	2	2
Energy Hedges [Member] \| Fair Value, Inputs, Level 2 [Member] \| Estimate of Fair Value Measurement [Member]
Derivative Liability	0	13
Interest Rate Swap [Member] \| Fair Value, Inputs, Level 2 [Member]
Derivative Liability	$ 3	$ 0

Total project debt.

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- Definition

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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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. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

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- Definition

Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

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Fair value of financial and nonfinancial obligations.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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