Commitments And Contingencies (Callaway Energy Center) (Parenthetical) (Detail) (USD $)	6 Months Ended
	Jun. 30, 2012 Week
Commitments And Contingencies [Line Items]
Threshold for which a retrospective assessment for a covered loss is necessary	$ 375,000,000
Annual payment in the event of an incident at any licensed commercial reactor	17,500,000
Aggregate maximum assessment per incident under Price-Anderson liability provisions of Atomic Energy Act	118,000,000
Maximum annual payment to be paid in a calendar year per reactor incident under liability provisions of Atomic Energy Act	17,500,000
Amount of primary property liability coverage	500,000,000
Amount of coverage in excess of primary property liability coverage	2,250,000,000
Losses in excess of primary coverage	500,000,000
Amount of weekly indemnity coverage commencing eight weeks after power outage	4,500,000
Number of weeks of coverage after the first eight weeks of an outage	52
Amount of additional weekly indemnity coverage commencing after initial indemnity coverage	3,600,000
Number of additional weeks after initial indemnity coverage for power outage, minimum	71
Amount of secondary weekly indemnity coverage for prolonged nuclear plant outage in excess of primary indemnity coverage	900,000
Replacement Power - Nuclear Electric Insurance Ltd [Member]
Commitments And Contingencies [Line Items]
Amount of weekly indemnity coverage thereafter not exceeding policy limit	490,000,000
Replacement Power - Energy Risk Assurance Company [Member]
Commitments And Contingencies [Line Items]
Amount of weekly indemnity coverage thereafter not exceeding policy limit	$ 3,600,000