Callaway Nuclear Plant (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
Mar. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Callaway Nuclear Plant [Abstract]
Number of mills charged for NWF fee	1
Assumed life of plant, in years	40
Annual decommissioning costs included in costs of service		$ 7	$ 7	$ 7

The average useful life of long-lived, physical assets used in the normal conduct of business and not intended for resale. Examples include land, buildings, machinery and equipment, and other types of furniture and equipment including, but not limited to, office equipment, furniture and fixtures, and computer equipment and software.

No definition available.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	duration