Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2011

Fair Value Disclosures [Abstract]

Schedule of Assets and Liabilities Measured at Fair Value on a Recurring Basis [Table Text Block]

The following tables summarize the Company's assets and liabilities that are measured at fair value on a recurring basis at September 30, 2011 and December 31, 2010 as well as reconcile the Company's commodity contracts fair value to PRM Assets and Liabilities on the Company's Condensed Consolidated Balance Sheets at September 30, 2011 and December 31, 2010.

September 30, 2011
(In millions)	Commodity Contracts						Gas Imbalances (A)
	Assets			Liabilities			Assets		Liabilities (B)
Quoted market prices in active market for identical assets (Level 1)	$	35.1		$	31.3		$	—	$	—
Significant other observable inputs (Level 2)	2.8			9.4			2.6		2.6
Significant unobservable inputs (Level 3)	1.5			—			—		—
Total fair value	39.4			40.7			2.6		2.6
Netting adjustments	(37.3		)	(33.7		)	—		—
Total	$	2.1		$	7.0		$	2.6	$	2.6
December 31, 2010
(In millions)	Commodity Contracts						Gas Imbalances (A)
	Assets			Liabilities			Assets		Liabilities (B)
Quoted market prices in active market for identical assets (Level 1)	$	20.6		$	20.2		$	—	$	—
Significant other observable inputs (Level 2)	2.7			30.7			2.5		2.8
Significant unobservable inputs (Level 3)	13.3			—			—		—
Total fair value	36.6			50.9			2.5		2.8
Netting adjustments	(34.4		)	(34.1		)	—		—
Total	$	2.2		$	16.8		$	2.5	$	2.8

(A) The Company uses the market approach to fair value its gas imbalance assets and liabilities, using an average of the Inside FERC Gas Market Report for Panhandle Eastern Pipe Line Co. (Texas, Oklahoma Mainline), ONEOK (Oklahoma) and ANR Pipeline (Oklahoma) indices.

(B) Gas imbalance liabilities exclude fuel reserves for over retained fuel due to shippers of $3.0 million and $3.9 million at September 30, 2011 and December 31, 2010, respectively, which fuel reserves are based on the value of natural gas at the time the imbalance was created and which are not subject to revaluation at fair market value.

Fair Value Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation [Table Text Block]

The following table summarizes the Company's assets and liabilities that are measured at fair value on a recurring basis using significant unobservable inputs (Level 3).

	Commodity Contracts
	Assets						Liabilities
(In millions)	2011			2010			2011		2010
Balance at January 1	$	13.3		$	49.0		$	—	$	14.7
Total gains or losses
Included in other comprehensive income	(4.8		)	(3.9		)	—		(5.1		)
Settlements	(3.3		)	(4.1		)	—		(1.4		)
Balance at March 31	5.2			41.0			—		8.2
Total gains or losses
Included in other comprehensive income	(1.0		)	7.2			—		(3.7		)
Settlements	(1.7		)	(6.1		)	—		(2.7		)
Balance at June 30	2.5			42.1			—		1.8
Total gains or losses
Included in other comprehensive income	0.4			(8.5		)	—		2.3
Settlements	(1.4		)	(6.7		)	—		(0.9		)
Balance at September 30	$	1.5		$	26.9		$	—	$	3.2

Schedule of Fair Value and Carrying Amount of PRM Financial Instruments [Table Text Block]

The following table summarizes the fair value and carrying amount of the Company's financial instruments, including derivative contracts related to the Company's PRM activities, at September 30, 2011 and December 31, 2010.

	September 30, 2011				December 31, 2010
	Carrying		Fair		Carrying		Fair
(In millions)	Amount		Value		Amount		Value
Price Risk Management Assets
Energy Derivative Contracts	$	2.1	$	2.1	$	2.2	$	2.2
Price Risk Management Liabilities
Energy Derivative Contracts	$	7.0	$	7.0	$	16.8	$	16.8
Long-Term Debt
OG&E Senior Notes	$	1,903.8	$	2,362.8	$	1,655.0	$	1,831.5
OGE Energy Senior Notes	99.6		109.7		99.7		106.4
OG&E Industrial Authority Bonds	135.4		135.4		135.4		135.4
Enogex LLC Senior Notes	448.1		502.7		447.8		480.7
Enogex LLC Revolving Credit Agreement	—		—		25.0		25.0