Risk Management and Fair Values (Derivative Instruments Designated as Cash Flow Hedges On Consolidated Statements Of Income) (Details) - Competitive Businesses Operating Revenues [Member] - Electricity Swaps And Options [Member] - Cash Flow Hedging [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Effect of Derivative instruments designated as cash flow hedges on consolidated statements of income
Amount of gain (loss) recognized in AOCI (effective portion)	$ 91	$ 50
Amount of gain reclassified from accumulated OCI into income (effective portion)	$ (30)	$ 51