Callaway Energy Center (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended	12 Months Ended
Jun. 30, 2012 kw	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Number of mills charged for NWF fee	1
Federal government fee for disposing of the spent nuclear fuel	0.001
Cost reimbursement under DOE settlement agreement	$ 1
Assumed life of plant, in years	40 years
Annual decommissioning costs included in costs of service		$ 7	$ 7	$ 7

Cash received for the settlement of litigation during the current period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 27

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 25

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3536-108585

Name:	us-gaap_ProceedsFromLegalSettlements
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration