Risk Management and Fair Values (Derivative Instruments Designated as Cash Flow Hedges On Consolidated Statements Of Income) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Effect of Derivative instruments designated as cash flow hedges on consolidated statements of income
Amount of gain reclassified from accumulated OCI into income (effective portion)	$ 4	$ 101	$ 2	$ 171
Competitive Businesses Operating Revenues [Member] | Electricity Swaps And Options [Member] | Cash Flow Hedging [Member]
Effect of Derivative instruments designated as cash flow hedges on consolidated statements of income
Amount of gain (loss) recognized in AOCI (effective portion)	54	(63)	(74)	228
Amount of gain reclassified from accumulated OCI into income (effective portion)	$ 4	$ 101	$ 2	$ 171