Commitments And Contingencies (Pumped-Storage Hydroelectric Facility Breach) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended			73 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011
Commitments And Contingencies [Abstract]
Payments relating to Taum Sauk incident damage and cleanup	$ 209
Payments relating to Taum Sauk incident damage and cleanup recorded to expense and not covered by insurance	1	1	2	37
Cumulative payments relating to Taum Sauk incident damage and cleanup covered by insurance and recorded as a receivable	172			172
Cumulative liability insurance reimbursements received for Taum Sauk incident	104
Insurance settlements receivable	$ 68			$ 68