Callaway Energy Center (Narrative) (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2014 mill	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Nuclear Waste Matters [Line Items]
Miscellaneous accounts and notes receivable	$ 117	$ 196
Nuclear Plant [Member]
Nuclear Waste Matters [Line Items]
Number of mills charged for NWF fee	1
Miscellaneous accounts and notes receivable	15	15
Assumed life of plant, in years	40 years
Annual decommissioning costs included in costs of service		$ 7	$ 7	$ 7
Minimum | Nuclear Plant [Member]
Nuclear Waste Matters [Line Items]
Number of mills charged for NWF fee	0