Callaway Energy Center (Narrative) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2015 mill	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2014
Nuclear Waste Matters [Line Items]
Miscellaneous accounts and notes receivable	$ 100			$ 81
Nuclear Plant [Member]
Nuclear Waste Matters [Line Items]
Number of mills charged for NWF fee	1
Miscellaneous accounts and notes receivable				15
Annual decommissioning costs included in costs of service	$ 7	$ 7	$ 7