Fair Value Measurements (Fair Value by Level) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Assets at fair value
Nuclear decommissioning trusts	$ 4,440	$ 4,242
SCE
Assets at fair value
Nuclear decommissioning trusts	$ 4,440	$ 4,242
Liabilities at fair value
Percentage of equity investments located in the United States (as a percent)	69.00%	70.00%
Collateralized mortgage obligations and other asset backed securities	$ 102	$ 79
Payables, net, related to investments	(59)	(127)
SCE \| Fair Value, Measurements, Recurring
Assets at fair value
Netting and Collateral	1
Total derivative contracts	110	74
Money market funds and other		33
Nuclear decommissioning trusts	4,499	4,369
Total assets	5,104	4,476
Liabilities at fair value
Derivative contracts	1	1,157
Netting and Collateral	2	0
Total liabilities	1	1,157
Net assets	5,103	3,319
SCE \| Fair Value, Measurements, Recurring \| Money market funds and other
Assets at fair value
Money market funds and other	495
SCE \| Fair Value, Measurements, Recurring \| Stocks
Assets at fair value
Nuclear decommissioning trusts	1,596	1,547
SCE \| Fair Value, Measurements, Recurring \| Fixed Income
Assets at fair value
Nuclear decommissioning trusts	2,730	2,616
SCE \| Fair Value, Measurements, Recurring \| Short-term investments, primarily cash equivalents
Assets at fair value
Nuclear decommissioning trusts	173	206
SCE \| Fair Value, Measurements, Recurring \| Level 1
Assets at fair value
Gross amounts recognized	0
Total derivative contracts		0
Money market funds and other		33
Nuclear decommissioning trusts	2,762	2,448
Total assets	3,257	2,481
Liabilities at fair value
Derivative contracts	0	0
Total liabilities	0	0
Net assets	3,257	2,481
SCE \| Fair Value, Measurements, Recurring \| Level 1 \| Money market funds and other
Assets at fair value
Money market funds and other	495
SCE \| Fair Value, Measurements, Recurring \| Level 1 \| Stocks
Assets at fair value
Nuclear decommissioning trusts	1,596	1,547
SCE \| Fair Value, Measurements, Recurring \| Level 1 \| Fixed Income
Assets at fair value
Nuclear decommissioning trusts	1,065	865
SCE \| Fair Value, Measurements, Recurring \| Level 1 \| Short-term investments, primarily cash equivalents
Assets at fair value
Nuclear decommissioning trusts	101	36
SCE \| Fair Value, Measurements, Recurring \| Level 2
Assets at fair value
Gross amounts recognized	9
Total derivative contracts		6
Money market funds and other		0
Nuclear decommissioning trusts	1,737	1,921
Total assets	1,746	1,927
Liabilities at fair value
Derivative contracts	2	0
Total liabilities	2	0
Net assets	1,744	1,927
SCE \| Fair Value, Measurements, Recurring \| Level 2 \| Money market funds and other
Assets at fair value
Money market funds and other	0
SCE \| Fair Value, Measurements, Recurring \| Level 2 \| Stocks
Assets at fair value
Nuclear decommissioning trusts	0	0
SCE \| Fair Value, Measurements, Recurring \| Level 2 \| Fixed Income
Assets at fair value
Nuclear decommissioning trusts	1,665	1,751
SCE \| Fair Value, Measurements, Recurring \| Level 2 \| Short-term investments, primarily cash equivalents
Assets at fair value
Nuclear decommissioning trusts	72	170
SCE \| Fair Value, Measurements, Recurring \| Level 3
Assets at fair value
Gross amounts recognized	102
Total derivative contracts		68
Money market funds and other		0
Nuclear decommissioning trusts	0	0
Total assets	102	68
Liabilities at fair value
Derivative contracts	1	1,157
Total liabilities	1	1,157
Net assets	101	(1,089)
SCE \| Fair Value, Measurements, Recurring \| Level 3 \| Money market funds and other
Assets at fair value
Money market funds and other	0
SCE \| Fair Value, Measurements, Recurring \| Level 3 \| Stocks
Assets at fair value
Nuclear decommissioning trusts	0	0
SCE \| Fair Value, Measurements, Recurring \| Level 3 \| Fixed Income
Assets at fair value
Nuclear decommissioning trusts	0	0
SCE \| Fair Value, Measurements, Recurring \| Level 3 \| Short-term investments, primarily cash equivalents
Assets at fair value
Nuclear decommissioning trusts	$ 0	$ 0

This element represents the collateralized mortgage obligations and other asset backed securities.

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- Definition

This element represents the percentage of equity investments located in United States.

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This element represents the fair value, Net, financial assets and liabilities as of the statement of financial position.

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Interest and dividends receivables and receivables related to pending securities sales and payables related to pending securities purchases as of the balance sheet date.

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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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- Definition

The fair value of investments held in a trust fund to pay for the costs of decontaminating and decommissioning facilities, whether such amount is presented as a separate caption or as a parenthetical disclosure on the balance sheet. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements.

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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, and obligation to return cash collateral under master netting arrangements.

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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.

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Fair value, before 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 elected not to be offset. Excludes assets 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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Fair value of asset associated with 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, and right to receive cash collateral under master netting arrangements.

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Fair value of financial and nonfinancial obligations.

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Fair value portion of other assets.

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