Fair Value Measurements (Details 1) (Level 3, USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2013		Dec. 31, 2012
Non Utility Generation Contract
Reconciliation of changes in the fair value of NUG contracts
Beginning Balance, Derivative Assets	$ 36	[1]	$ 57	[1]
Beginning Balance, Derivative Liabilities	(290)	[1]	(349)	[1]
Beginning Balance, Net	(254)	[1]	(292)	[1]
Unrealized gain (loss), Derivative Assets	0	[1]	(20)	[1]
Unrealized gain (loss), Derivative Liabilities	18	[1]	(180)	[1]
Unrealized gain (loss), Net	18	[1]	(200)	[1]
Purchases, Derivative Assets			0	[1]
Purchases, Derivative Liabilities			0	[1]
Purchases, Net			0	[1]
Settlements, Derivative Assets	(2)	[1]	(1)	[1]
Settlements, Derivative Liabilities	25	[1]	239	[1]
Settlements, Net	23	[1]	238	[1]
Ending Balance, Derivative Assets	34	[1]	36	[1]
Ending Balance, Derivative Liabilities	(247)	[1]	(290)	[1]
Ending Balance, Net	(213)	[1]	(254)	[1]
LCAPP Contracts
Reconciliation of changes in the fair value of NUG contracts
Beginning Balance, Derivative Assets	0	[1]	0	[1]
Beginning Balance, Derivative Liabilities	(144)	[1]	0	[1]
Beginning Balance, Net	(144)	[1]	0	[1]
Unrealized gain (loss), Derivative Assets	0	[1]	0	[1]
Unrealized gain (loss), Derivative Liabilities	(2)	[1]	1	[1]
Unrealized gain (loss), Net	(2)	[1]	1	[1]
Purchases, Derivative Assets			0	[1]
Purchases, Derivative Liabilities			(145)	[1]
Purchases, Net			(145)	[1]
Settlements, Derivative Assets	0	[1]	0	[1]
Settlements, Derivative Liabilities	0	[1]	0	[1]
Settlements, Net	0	[1]	0	[1]
Ending Balance, Derivative Assets	0	[1]	0	[1]
Ending Balance, Derivative Liabilities	(146)	[1]	(144)	[1]
Ending Balance, Net	(146)	[1]	(144)	[1]
FTRs
Reconciliation of changes in the fair value of NUG contracts
Beginning Balance, Derivative Assets	8		1
Beginning Balance, Derivative Liabilities	(9)		(23)
Beginning Balance, Net	(1)		(22)
Unrealized gain (loss), Derivative Assets	0		6
Unrealized gain (loss), Derivative Liabilities	1		(6)
Unrealized gain (loss), Net	1		0
Purchases, Derivative Assets			13
Purchases, Derivative Liabilities			(10)
Purchases, Net			3
Settlements, Derivative Assets	(6)		(12)
Settlements, Derivative Liabilities	3		30
Settlements, Net	(3)		18
Ending Balance, Derivative Assets	2		8
Ending Balance, Derivative Liabilities	(5)		(9)
Ending Balance, Net	(3)		(1)
FTRs | FES
Reconciliation of changes in the fair value of NUG contracts
Beginning Balance, Derivative Assets	6		1
Beginning Balance, Derivative Liabilities	(6)		(7)
Beginning Balance, Net	0		(6)
Unrealized gain (loss), Derivative Assets			4
Unrealized gain (loss), Derivative Liabilities			(4)
Unrealized gain (loss), Net			0
Purchases, Derivative Assets			9
Purchases, Derivative Liabilities			(7)
Purchases, Net			2
Settlements, Derivative Assets	(4)		(8)
Settlements, Derivative Liabilities	2		12
Settlements, Net	(2)		4
Ending Balance, Derivative Assets	2		6
Ending Balance, Derivative Liabilities	(4)		(6)
Ending Balance, Net	$ (2)		$ 0

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