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		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 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	$ (53)	$ 93	$ 86
Amount of gain reclassified from accumulated OCI into income (effective portion)	$ 13	$ 46	$ 64	$ 200