Fair Value Measurements (Fair Value by Level) (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Assets at fair value
Nuclear decommissioning trusts	$ 4,330	$ 4,440
Southern California Edison
Assets at fair value
Nuclear decommissioning trusts	$ 4,330	$ 4,440
Liabilities at fair value
Percentage of equity investments located in the United States	72.00%	69.00%
Collateralized mortgage obligations and other asset backed securities	$ 72	$ 102
Payables, net, related to investments	182	59
Southern California Edison \| Fair Value, Measurements, Recurring
Assets at fair value
Netting and Collateral	(8)	(1)
Derivative contracts, net	79	110
Other	36	495
Nuclear decommissioning trusts	4,512	4,499
Total assets	4,627	5,104
Liabilities at fair value
Netting and Collateral	(20)	(2)
Derivative contracts	8	1
Total liabilities	8	1
Total assets, netting and collateral	12	1
Net assets	4,619	5,103
Southern California Edison \| Fair Value, Measurements, Recurring \| Stocks
Assets at fair value
Nuclear decommissioning trusts	1,600	1,596
Southern California Edison \| Fair Value, Measurements, Recurring \| Fixed Income
Assets at fair value
Nuclear decommissioning trusts	2,676	2,730
Southern California Edison \| Fair Value, Measurements, Recurring \| Short-term investments, primarily cash equivalents
Assets at fair value
Nuclear decommissioning trusts	236	173
Southern California Edison \| Fair Value, Measurements, Recurring \| Level 1
Assets at fair value
Derivative contracts	0	0
Other	15	495
Nuclear decommissioning trusts	2,769	2,762
Total assets	2,784	3,257
Liabilities at fair value
Derivative contracts	0	0
Total liabilities	0	0
Net assets	2,784	3,257
Southern California Edison \| Fair Value, Measurements, Recurring \| Level 1 \| Stocks
Assets at fair value
Nuclear decommissioning trusts	1,600	1,596
Southern California Edison \| Fair Value, Measurements, Recurring \| Level 1 \| Fixed Income
Assets at fair value
Nuclear decommissioning trusts	1,025	1,065
Southern California Edison \| Fair Value, Measurements, Recurring \| Level 1 \| Short-term investments, primarily cash equivalents
Assets at fair value
Nuclear decommissioning trusts	144	101
Southern California Edison \| Fair Value, Measurements, Recurring \| Level 2
Assets at fair value
Derivative contracts	56	9
Other	21	0
Nuclear decommissioning trusts	1,743	1,737
Total assets	1,820	1,746
Liabilities at fair value
Derivative contracts	28	2
Total liabilities	28	2
Net assets	1,792	1,744
Southern California Edison \| Fair Value, Measurements, Recurring \| Level 2 \| Stocks
Assets at fair value
Nuclear decommissioning trusts	0	0
Southern California Edison \| Fair Value, Measurements, Recurring \| Level 2 \| Fixed Income
Assets at fair value
Nuclear decommissioning trusts	1,651	1,665
Southern California Edison \| Fair Value, Measurements, Recurring \| Level 2 \| Short-term investments, primarily cash equivalents
Assets at fair value
Nuclear decommissioning trusts	92	72
Southern California Edison \| Fair Value, Measurements, Recurring \| Level 3
Assets at fair value
Derivative contracts	31	102
Other	0	0
Nuclear decommissioning trusts	0	0
Total assets	31	102
Liabilities at fair value
Derivative contracts	0	1
Total liabilities	0	1
Net assets	31	101
Southern California Edison \| Fair Value, Measurements, Recurring \| Level 3 \| Stocks
Assets at fair value
Nuclear decommissioning trusts	0	0
Southern California Edison \| Fair Value, Measurements, Recurring \| Level 3 \| Fixed Income
Assets at fair value
Nuclear decommissioning trusts	0	0
Southern California Edison \| Fair Value, Measurements, Recurring \| Level 3 \| Short-term investments, primarily cash equivalents
Assets at fair value
Nuclear decommissioning trusts	$ 0	$ 0

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

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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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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, 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 asset after deduction of liability.

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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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