Callaway Energy Center (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Loss Contingencies [Line Items]
Number of mills charged for NWF fee	1
Costs incurred to be recovered	$ 13
Settlement payment	11
Annual decommissioning costs included in costs of service	7	7	7
Reduction To Depreciation And Amortization [Member]
Loss Contingencies [Line Items]
Settlement payment	2
Reduction To Other Operations And Maintenance [Member]
Loss Contingencies [Line Items]
Settlement payment	2
Reduction In Property And Plant [Member]
Loss Contingencies [Line Items]
Settlement payment	$ 7