Regulatory Assets, Liabilities, And Balancing Accounts (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Regulatory Assets [Line Items]
Deferred income taxes regulatory asset recovery maximum (years)	47 years
Utility retained generation asset costs	$ 1,200
Weighted average remaining life of Utility retained generation assets (years)	10 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)	11 years
Current regulatory liabilities	$ 676	$ 261
Current regulatory assets	517	$ 444
Bill Credit to Natural Gas Customers	$ 400