Investments (Nuclear Decommissioning Trusts) (Details) - SCE - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Investment Holdings [Line Items]
Unrealized holding gains, net of losses	$ 2,000	$ 2,100
Deferred income taxes related to unrealized gains	477	515
Nuclear decommissioning trusts	$ 4,300	$ 4,300

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