Regulatory Assets, Liabilities, And Balancing Accounts (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Regulatory Assets [Line Items]
Utility retained generation asset costs	$ 1,200
Weighted average remaining life of Utility retained generation assets (years)	9 years
Environmental compliance costs regulatory asset recovery (years)	32 years
Price risk management regulatory assets recovery (years)	10 years
Recovery of costs related to debt reacquired or redeemed prior to maturity (years)	25 years
Current regulatory assets	$ 615	$ 423
CEMA [Member]
Regulatory Assets [Line Items]
Current regulatory assets	$ 426	$ 223