Fair Value Measurements of Assets and Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Long-term debt	$ 2,435	$ 2,383
Project Debt	127	133
Estimate of Fair Value Measurement [Member]
Assets, Fair Value Disclosure	4	14
Financial and Nonfinancial Liabilities, Fair Value Disclosure	10	2
Long-term debt	2,464	2,459
Project Debt	132	138
Reported Value Measurement [Member]
Long-term debt	2,435	2,383
Project Debt	127	133
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 Asset	2
Energy Hedges [Member] \| Fair Value, Inputs, Level 2 [Member] \| Energy Hedges [Member] \| Estimate of Fair Value Measurement [Member]
Derivative Asset		12
Interest Rate Swap [Member] \| Fair Value, Inputs, Level 2 [Member]
Derivative Liability	$ 10	$ 2

Total project debt.

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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 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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