Risk Management and Fair Values (Derivative Instruments Designated as Cash Flow Hedges On Consolidated Statements Of Income) (Details) - Competitive Businesses Operating Revenues [Member] - Electricity Futures Forwards Swaps And Options [Member] - Cash Flow Hedging [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Effect of Derivative instruments designated as cash flow hedges on consolidated statements of income
Amount of gain (loss) recognized in AOCI (effective portion)	$ (40)	$ 44	$ 135
Amount of gain reclassified from accumulated OCI into income (effective portion)	$ (68)	$ 109	$ 293