Risk Management and Fair Values (Narrative) (Details) (USD $)	0 Months Ended	3 Months Ended
	Mar. 31, 2012 Y	Dec. 31, 2012	Mar. 31, 2012 Y	Mar. 31, 2011
Risk Management and Fair Values [Abstract]
Cash flow hedges relating to power sales as part of net unrealized gains	$ 528,000,000
Reclassified from accumulated other comprehensive income (OCI) to operating revenues			332,000,000
Gains on maturity of cash flow hedges, before taxes			71,000,000	29,000,000
Gains on maturity of cash flow hedges, Tax			25,000,000	10,000,000
Maximum length of time over which Company is currently hedging the variability in future cash flows for forecasted power transactions, years	2.75		2.75
Planned generation sold forward from non utility nuclear power plants in the next three quarters		89.00%
Planned Generation Sold Forward under financial derivatives	44.00%		44.00%
Total volume of natural gas swaps outstanding (MMBtu)	56,330,000		56,330,000
Cash flow hedges in-the-money contracts	$ 528,000,000		$ 528,000,000