Variable Interest Entities (Trusts) (Details)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021 USD ($) MW	Sep. 30, 2020 USD ($) MW	Sep. 30, 2021 USD ($) MW	Sep. 30, 2020 USD ($) MW	Dec. 31, 2017 USD ($) $ / shares	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2020 USD ($)
Variable Interest Entity [Line Items]
Redemption of trust securities		$ 308,000,000
SCE
Variable Interest Entity [Line Items]
Common stock	$ 2,168,000,000		$ 2,168,000,000							$ 2,168,000,000
Redemption of trust securities		$ 308,000,000
SCE | Trust Securities [Member]
Variable Interest Entity [Line Items]
Liquidation value (in dollars per share) | $ / shares					$ 2,500
SCE | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Liquidation value (in dollars per share) | $ / shares					$ 25
Common stock	$ 10,000		$ 10,000		$ 10,000					10,000
SCE | Power Purchase Agreements
Variable Interest Entity [Line Items]
Power generating capacity for majority interest (in megawatts) | MW	3,455	5,356	3,455	5,356
Amount of related party transaction	$ 248,000,000	$ 360,000,000	$ 519,000,000	$ 661,000,000
SCE | Trust II
Variable Interest Entity [Line Items]
Liquidation preference									$ 400,000,000
SCE | Trust II | Trust Securities [Member]
Variable Interest Entity [Line Items]
Liquidation preference	220,000,000		220,000,000							220,000,000
SCE | Trust II | 5.10% Series G (cumulative)
Variable Interest Entity [Line Items]
Security dividend rate, (as a percent)									5.10%
Liquidation preference	220,000,000		220,000,000						$ 400,000,000	220,000,000
SCE | Trust III
Variable Interest Entity [Line Items]
Liquidation preference								$ 275,000,000
SCE | Trust III | Trust Securities [Member]
Variable Interest Entity [Line Items]
Liquidation preference	275,000,000		275,000,000							275,000,000
SCE | Trust III | 5.75% Series H (cumulative)
Variable Interest Entity [Line Items]
Security dividend rate, (as a percent)								5.75%
Liquidation preference	275,000,000		275,000,000					$ 275,000,000		275,000,000
SCE | Trust IV
Variable Interest Entity [Line Items]
Liquidation preference							$ 325,000,000
SCE | Trust IV | Trust Securities [Member]
Variable Interest Entity [Line Items]
Liquidation preference	325,000,000		325,000,000							325,000,000
SCE | Trust IV | 5.375% Series J (cumulative)
Variable Interest Entity [Line Items]
Security dividend rate, (as a percent)							5.375%
Liquidation preference	325,000,000		325,000,000				$ 325,000,000			325,000,000
SCE | Trust V
Variable Interest Entity [Line Items]
Liquidation preference						$ 300,000,000
SCE | Trust V | Trust Securities [Member]
Variable Interest Entity [Line Items]
Liquidation preference	300,000,000		300,000,000							300,000,000
SCE | Trust V | 5.45% Series K (cumulative)
Variable Interest Entity [Line Items]
Security dividend rate, (as a percent)						5.45%
Liquidation preference	300,000,000		300,000,000			$ 300,000,000				300,000,000
SCE | Trust VI
Variable Interest Entity [Line Items]
Liquidation preference					$ 475,000,000
SCE | Trust VI | Trust Securities [Member]
Variable Interest Entity [Line Items]
Liquidation preference	475,000,000		475,000,000							475,000,000
SCE | Trust VI | 5.00% Series L (cumulative)
Variable Interest Entity [Line Items]
Security dividend rate, (as a percent)					5.00%
Liquidation preference	$ 475,000,000		$ 475,000,000		$ 475,000,000					$ 475,000,000