Income Taxes (Net Operating Loss and Tax Credit Carryforwards) (Details) $ in Millions	Dec. 31, 2017 USD ($)
Tax Credit Carryforward [Line Items]
Loss Carryforwards, Expiring 2018 to 2036	$ 901
Loss Carryforwards, No expiration date	0
Loss Carryforwards	901
Credit Carryforward, Expiring 2018 to 2036	451
Credit Carryforward, No expiration date	71
Credit Carryforwards	522
SCE
Tax Credit Carryforward [Line Items]
Loss Carryforwards, Expiring 2018 to 2036	162
Loss Carryforwards, No expiration date	0
Loss Carryforwards	162
Credit Carryforward, Expiring 2018 to 2036	25
Credit Carryforward, No expiration date	38
Credit Carryforwards	$ 63