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		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Effect of Derivative instruments designated as cash flow hedges on consolidated statements of income
Amount of gain (loss) recognized in AOCI (effective portion)	$ 43	$ 70	$ 136	$ 156
Amount of gain reclassified from accumulated OCI into income (effective portion)	$ 23	$ 37	$ 87	$ 237