Price Risk Management (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Derivative [Line Items]
Derivative Liability	$ (4)
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	88	$ 136
Derivative, Collateral, Right to Reclaim Cash	11	11
Net gain or loss recognized in the statement of income offset by regulatory accounting	18	82	$ 13
Derivative, Net Liability Position, Aggregate Fair Value	144
Collateral Already Posted, Aggregate Fair Value	48
Collateral Aggregate Fair Value	136
Margin Deposit Assets	0
Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	170
Electricity [Member]
Derivative [Line Items]
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	84	130
Natural Gas [Member]
Derivative [Line Items]
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	$ 4	$ 6

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

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-Publisher SEC
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-Section 13
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The aggregate fair value of assets that would be required to be posted as collateral for derviative instruments with credit-risk-related contingent features if the credit-risk-related contingent features were triggered at the end of the reporting period.

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Net gain or loss recognized in the statement of income for derivative instruments related to price risk management activities offset by regulatory accounting.

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The aggregate fair value of assets that are already posted, at the end of the reporting period, as collateral for derivative instruments with credit-risk-related contingent features.

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The carrying amount of the asset transferred to a third party to serve as a deposit, which typically serves as security against failure by the transferor to perform under terms of an agreement.

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Amount of right to receive cash collateral under master netting arrangements that have not been offset against derivative liabilities.

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Fair value, after offset of derivative asset, of 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, elected not to be and before offset against a right to receive collateral under a master netting arrangement. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

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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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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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The aggregate fair value amounts of derivative instruments that contain credit-risk-related contingent features that are in a net liability position at the end of the reporting period. For nonderivative instruments that are designated and qualify as hedging instruments, the fair value amounts are the carrying value of the nonderivative hedging instrument, including the adjustment for the foreign currency transaction gain (loss) on that instrument.

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