Fair Value Measurements (Details 2) (Level 3, USD $) In Millions, unless otherwise specified																							6 Months Ended
	Jun. 30, 2013 FTRs	Dec. 31, 2012 FTRs	Dec. 31, 2011 FTRs	Jun. 30, 2013 FTRs FES	Dec. 31, 2012 FTRs FES	Dec. 31, 2011 FTRs FES	Jun. 30, 2013 Non Utility Generation Contract		Dec. 31, 2012 Non Utility Generation Contract		Dec. 31, 2011 Non Utility Generation Contract		Jun. 30, 2013 LCAPP Contracts		Dec. 31, 2012 LCAPP Contracts		Dec. 31, 2011 LCAPP Contracts		Jun. 30, 2013 Model FTRs	Jun. 30, 2013 Model FTRs FES	Jun. 30, 2013 Model Non Utility Generation Contract	Jun. 30, 2013 Model LCAPP Contracts	Jun. 30, 2013 Model Minimum FTRs	Jun. 30, 2013 Model Minimum FTRs FES	Jun. 30, 2013 Model Minimum Non Utility Generation Contract MWh	Jun. 30, 2013 Model Minimum LCAPP Contracts	Jun. 30, 2013 Model Maximum FTRs	Jun. 30, 2013 Model Maximum FTRs FES	Jun. 30, 2013 Model Maximum Non Utility Generation Contract MWh	Jun. 30, 2013 Model Maximum LCAPP Contracts	Jun. 30, 2013 Model Weighted Average FTRs	Jun. 30, 2013 Model Weighted Average FTRs FES	Jun. 30, 2013 Model Weighted Average Non Utility Generation Contract MWh	Jun. 30, 2013 Model Weighted Average LCAPP Contracts
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value	$ (2)	$ (1)	$ (22)	$ (3)	$ 0	$ (6)	$ (232)	[1]	$ (254)	[1]	$ (292)	[1]	$ (158)	[1]	$ (144)	[1]	$ 0	[1]	$ (2)	$ (3)	$ (232)	$ (158)
Fair Value Inputs, RTO Auction Clearing Prices																							(4.1)	(4.1)			6.4	5.7			0.80	0.60
Fair Value Inputs, Power																									700				6,087,000				1,522,000
Fair Value Inputs, Power, Regional Prices																									48.80	158.60			57.3	187.60			52.30	171.20

[1] Changes in the fair value of NUG and LCAPP contracts are generally subject to regulatory accounting treatment and do not impact earnings.