Summary of Significant Accounting Policies (Prepaid Insurance) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Sep. 30, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Redeemable Noncontrolling Interest [Line Items]
Wildfire Insurance Fund contributions long term			$ 2,400	$ 2,800
Wildfire Insurance Fund contributions current			323	323
Wildfire Insurance Fund contributions			95	2,457	$ 0
Insurance fund liability included in other long-term liabilities			$ 703	785
Amortization period			10 years
Subsequent event
Redeemable Noncontrolling Interest [Line Items]
Amortization period	15 years
Measurement Input
Redeemable Noncontrolling Interest [Line Items]
Historical term used in estimate			5 years
Measurement Input | Subsequent event
Redeemable Noncontrolling Interest [Line Items]
Historical term used in estimate	7 years
SCE
Redeemable Noncontrolling Interest [Line Items]
Wildfire Insurance Fund contributions long term			$ 2,400	2,800
Wildfire Insurance Fund contributions current			323	323
Wildfire Insurance Fund contributions		$ 2,400	95	2,457	$ 0
Insurance fund liability included in other long-term liabilities			$ 703	$ 785
Amortization period			10 years