Income Taxes Income tax expense (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended							12 Months Ended			12 Months Ended				12 Months Ended		12 Months Ended		12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009		Dec. 31, 2011 Operating Loss [Member]	Dec. 31, 2030 State operating loss [Member]	Dec. 31, 2011 State operating loss [Member]	Dec. 31, 2011 Oklahoma investment tax credits [Member]	Dec. 31, 2015 Oklahoma capital investment board credits [Member]		Dec. 31, 2011 Oklahoma capital investment board credits [Member]		Dec. 31, 2030 Federal operating loss [Member]	Dec. 31, 2011 Federal operating loss [Member]	Dec. 31, 2029 Federal tax credits [Member]	Dec. 31, 2011 Federal tax credits [Member]	Dec. 31, 2020 Oklahoma zero emission tax credits [Member]	Dec. 31, 2011 Oklahoma zero emission tax credits [Member]
Federal	$ (6.4)		$ 15.8		$ (145.3)
State	0		2.3		(4.8)
Total Provision (Benefit) for Current Income Taxes	(6.4)		18.1		(150.1)
Federal	160.3		134.5		256.7
State	2.9		9.3		8.1
Total Provision for Deferred Income Taxes, net	163.2		143.8		264.8
Deferred Federal Investment Tax Credits, net	(3.3)		(3.7)		(4.2)
Income Taxes Relating to Other Income and Deductions	7.2		2.8		10.6
Income Tax Expense (Benefit)	160.7		161.0		121.1
Statutory Federal tax rate	35.00%		35.00%		35.00%
Amortization of net unfunded deferred taxes	0.70%		0.70%		0.70%
State income taxes, net of Federal income tax benefit	0.60%		1.70%		1.00%
Medicare Part D subsidy	0.20%		2.60%		(1.10%)
Qualified production activities	0.00%		(0.20%)		0.00%
401(k) dividends	(0.50%)		(0.60%)		(0.70%)
Federal investment tax credits, net	(0.70%)		(0.80%)		(1.10%)
Income attributable to noncontrolling interest	(1.30%)		(0.40%)		0.00%
Federal renewable energy credit	(3.40%)	[1]	(3.40%)	[1]	(2.20%)	[1]
Other	0.10%		0.30%		0.10%
Effective income tax rate	30.70%		34.90%		31.70%
Net operating losses	15.8		0
Accrued labilities	13.2		8.2
Accrued vacation	4.2		6.1
Uncollectible accounts	1.4		0.6
Other	0		2.8
Total Current Deferred Income Tax Assets	34.6		17.7
Derivative instruments	(2.5)		1.0
Total Current Accrued Income Tax Liabilities	(2.5)		1.0
Current Deferred Income Tax Assets, net	32.1		18.7
Accelerated depreciation and other property related differences	1,449.6		1,071.4
Investment in Enogex Holdings	571.8		376.1
Company pension plan	67.5		71.4
Regulatory asset	21.2		17.2
Income taxes refundable to customers, net	15.9		16.8
Bond redemption - unamortized costs	4.4		4.8
Derivative instruments	0		22.4
Total Non-Current Deferred Income Tax Liabilities	2,130.4		1,580.1
Net operating losses	(225.2)		0
Regulatory liabilities	(65.3)		(43.7)
State tax credits	(63.0)		(35.5)
Postretirement medical and life insurance benefits	(50.2)		(39.0)
Federal tax credits	(49.7)		(21.5)
Derivative instruments	(12.8)		0
Deferred Federal investment tax credits	(2.3)		(3.6)
Other	(10.5)		(2.0)
Total Non-Current Deferred Income Tax Assets	(479.0)		(145.3)
Non-Current Deferred Income Tax Liabilities, net	1,651.4		1,434.8
Tax Credit Carryforward Amount							45.0		772.9	76.3			7.3	[2]		607.2		49.7		8.4
Tax Credit Carryforward Deferred Tax Asset									28.4	49.7			7.3	[2]		212.6		49.7		6.0
Tax Credit Carryforward Expiration Dates								2030			2015	[2]			2030		2029		2020
Unrecognized Tax Benefits	$ 0		$ 0

[1] (A) These are credits associated with the production from OG&E's wind farms.

[2] (A) Oklahoma capital investment board credits may not be exercisable after July 1, 2015. The Company anticipates the credits will be monetized or the expiration date of these credits will be extended.