Commitments And Contingencies (Callaway Energy Center) (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015
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	19,000,000
Aggregate maximum assessment per incident under Price-Anderson liability provisions of Atomic Energy Act	128,000,000
Maximum annual payment in calendar year per reactor incident under Price Andersen Liability Provisions of Atomic Energy Act	19,000,000
Amount of weekly indemnity coverage commencing eight weeks after power outage	4,500,000.0
Number of weeks of coverage after the first eight weeks of an outage	1 year
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	1 year 4 months 10 days
Inflationary adjustment prescribed by most recent Price-Anderson Act renewal, in years	5 years
Aggregate nuclear power industry insurance policy limit for losses from terrorist attacks within twelve month period	3,240,000,000
Public Liability
Commitments And Contingencies [Line Items]
Maximum Coverages	13,616,000,000	[1]
Maximum Assessments for Single Incidents	128,000,000
Public Liability And Nuclear Worker Liability - American Nuclear Insurers [Member]
Commitments And Contingencies [Line Items]
Maximum Coverages	375,000,000
Maximum Assessments for Single Incidents	0
Public Liability And Nuclear Worker Liability - Pool Participation [Member]
Commitments And Contingencies [Line Items]
Maximum Coverages	13,241,000,000	[2]
Maximum Assessments for Single Incidents	128,000,000	[3]
Property Damage
Commitments And Contingencies [Line Items]
Maximum Coverages	3,250,000,000
Maximum Assessments for Single Incidents	26,000,000
Property Damage - Nuclear Electric Insurance Ltd [Member]
Commitments And Contingencies [Line Items]
Maximum Coverages	2,750,000,000	[4]
Maximum Assessments for Single Incidents	26,000,000	[5]
Property Damage European Mutual Association for Nuclear Insurance [Member]
Commitments And Contingencies [Line Items]
Maximum Coverages	500,000,000	[6]
Replacement Power - Nuclear Electric Insurance Ltd [Member]
Commitments And Contingencies [Line Items]
Maximum Coverages	490,000,000	[7]
Maximum Assessments for Single Incidents	9,000,000	[5]
Amount of weekly indemnity coverage thereafter not exceeding policy limit	490,000,000
Sub-limit of for non-nuclear events	328,000,000
Non-radiation event [Member]
Commitments And Contingencies [Line Items]
Maximum Coverages	2,250,000,000
Aggregate nuclear power industry insurance policy limit for losses from terrorist attacks within twelve month period	1,830,000,000
Radiation Event [Member]
Commitments And Contingencies [Line Items]
Maximum Coverages	$ 500,000,000

[1] Limit of liability for each incident under the Price-Anderson liability provisions of the Atomic Energy Act of 1954, as amended. A company could be assessed up to $128 million per incident for each licensed reactor it operates with a maximum of $19 million per incident to be paid in a calendar year for each reactor. This limit is subject to change to account for the effects of inflation and changes in the number of licensed reactors.

[2] Provided through mandatory participation in an industrywide retrospective premium assessment program.

[3] Retrospective premium under the Price-Anderson Act. This is subject to retrospective assessment with respect to a covered loss in excess of $375 million in the event of an incident at any licensed United States commercial reactor, payable at $19 million per year.

[4] provides $2.25 billion in property damage, decontamination, and premature decommissioning insurance for both radiation and nonradiation events.

[5] All NEIL insured plants could be subject to assessments should losses exceed the accumulated funds from NEIL.

[6] European Mutual Association for Nuclear Insurance provides $500 million in excess of the $2.75 billion and $2.25 billion property coverage for radiation and nonradiation events, respectively, provided by NEIL.

[7] Provides replacement power cost insurance in the event of a prolonged accidental outage. Weekly indemnity up to $4.5 million for 52 weeks, which commences after the first twelve weeks of an outage, plus up to $3.6 million per week for a minimum of 71 weeks thereafter for a total not exceeding the policy limit of $490 million. Nonradiation events are sub-limited to $328 million.