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, 2020	Dec. 31, 2019	Dec. 31, 2018
Effect of Derivative instruments designated as cash flow hedges on consolidated statements of income
Amount of gain (loss) recognized in AOCI (effective portion)	$ 77	$ 232	$ (40)
Amount of gain reclassified from accumulated OCI into income (effective portion)	$ 148	$ 97	$ (68)