Variable Interest Entities (Textual) (Details)	1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Jul. 31, 2017 USD ($)	Sep. 30, 2018 USD ($) $ / shares MW	Sep. 30, 2017 USD ($) MW	Sep. 30, 2018 USD ($) $ / shares MW	Sep. 30, 2017 USD ($) MW	Dec. 31, 2017 USD ($) $ / shares	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012 USD ($)
Variable Interest Entity
Redemption of trust securities					$ 475,000,000
Southern California Edison
Variable Interest Entity
Redemption of trust securities					$ 475,000,000
Southern California Edison | Variable Interest Entity, Not Primary Beneficiary | SCE Power Purchase Contracts
Variable Interest Entity
Power generating capacity (in megawatts) | MW		3,602	4,858	3,602	4,858
Payments to unconsolidated VIEs for power purchase contracts		$ 328,000,000	$ 325,000,000	$ 567,000,000	$ 571,000,000
Southern California Edison | Variable Interest Entity, Not Primary Beneficiary | Trust I | Trust Securities
Variable Interest Entity
Security dividend rate											5.625%
Liquidation preference	$ 475,000,000										$ 475,000,000
Redemption of trust securities	$ 10,000					$ 10,000					10,000
Southern California Edison | Variable Interest Entity, Not Primary Beneficiary | Trust I | Series F Preferred Stock
Variable Interest Entity
Liquidation preference											$ 475,000,000
Southern California Edison | Variable Interest Entity, Not Primary Beneficiary | Trust II
Variable Interest Entity
Common stock		10,000		10,000		10,000
Southern California Edison | Variable Interest Entity, Not Primary Beneficiary | Trust II | Trust Securities
Variable Interest Entity
Security dividend rate										5.10%
Liquidation preference		$ 400,000,000		$ 400,000,000		$ 400,000,000
Liquidation value (in dollars per share) | $ / shares		$ 25		$ 25		$ 25
Common stock						$ 10,000
Southern California Edison | Variable Interest Entity, Not Primary Beneficiary | Trust II | Series F Preferred Stock
Variable Interest Entity
Liquidation value (in dollars per share) | $ / shares						$ 2,500
Southern California Edison | Variable Interest Entity, Not Primary Beneficiary | Trust II | Series G Preferred Stock
Variable Interest Entity
Security dividend rate				5.10%
Liquidation preference		$ 400,000,000		$ 400,000,000		$ 400,000,000
Liquidation value (in dollars per share) | $ / shares		$ 2,500		$ 2,500
Southern California Edison | Variable Interest Entity, Not Primary Beneficiary | Trust III
Variable Interest Entity
Common stock		$ 10,000		$ 10,000		10,000
Southern California Edison | Variable Interest Entity, Not Primary Beneficiary | Trust III | Trust Securities
Variable Interest Entity
Security dividend rate									5.75%
Liquidation preference		$ 275,000,000		$ 275,000,000		275,000,000
Liquidation value (in dollars per share) | $ / shares		$ 25		$ 25
Southern California Edison | Variable Interest Entity, Not Primary Beneficiary | Trust III | Series H Preferred Stock
Variable Interest Entity
Security dividend rate				5.75%
Liquidation preference		$ 275,000,000		$ 275,000,000		275,000,000
Liquidation value (in dollars per share) | $ / shares		$ 2,500		$ 2,500
Southern California Edison | Variable Interest Entity, Not Primary Beneficiary | Trust IV
Variable Interest Entity
Common stock		$ 10,000		$ 10,000		10,000
Southern California Edison | Variable Interest Entity, Not Primary Beneficiary | Trust IV | Trust Securities
Variable Interest Entity
Security dividend rate								5.375%
Liquidation preference		$ 325,000,000		$ 325,000,000		325,000,000
Liquidation value (in dollars per share) | $ / shares		$ 25		$ 25
Southern California Edison | Variable Interest Entity, Not Primary Beneficiary | Trust IV | Series J Preferred Stock
Variable Interest Entity
Security dividend rate				5.375%
Liquidation preference		$ 325,000,000		$ 325,000,000		325,000,000
Liquidation value (in dollars per share) | $ / shares		$ 2,500		$ 2,500
Southern California Edison | Variable Interest Entity, Not Primary Beneficiary | Trust V
Variable Interest Entity
Common stock		$ 10,000		$ 10,000		10,000
Southern California Edison | Variable Interest Entity, Not Primary Beneficiary | Trust V | Trust Securities
Variable Interest Entity
Security dividend rate							5.45%
Liquidation preference		$ 300,000,000		$ 300,000,000		300,000,000
Liquidation value (in dollars per share) | $ / shares		$ 25		$ 25
Southern California Edison | Variable Interest Entity, Not Primary Beneficiary | Trust V | Series K Preferred Stock
Variable Interest Entity
Security dividend rate				5.45%
Liquidation preference		$ 300,000,000		$ 300,000,000		300,000,000
Liquidation value (in dollars per share) | $ / shares		$ 2,500		$ 2,500
Southern California Edison | Variable Interest Entity, Not Primary Beneficiary | Trust VI
Variable Interest Entity
Common stock		$ 10,000		$ 10,000		$ 10,000
Southern California Edison | Variable Interest Entity, Not Primary Beneficiary | Trust VI | Trust Securities
Variable Interest Entity
Security dividend rate						5.00%
Liquidation preference		$ 475,000,000		$ 475,000,000		$ 475,000,000
Liquidation value (in dollars per share) | $ / shares		$ 25		$ 25
Southern California Edison | Variable Interest Entity, Not Primary Beneficiary | Trust VI | Series L Preferred Stock
Variable Interest Entity
Security dividend rate				5.00%
Liquidation preference		$ 475,000,000		$ 475,000,000		$ 475,000,000
Liquidation value (in dollars per share) | $ / shares		$ 2,500		$ 2,500