Income Taxes (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Current Federal Tax Expense (Benefit)		$ 0.0	$ 0.0	$ 0.0
Current State and Local Tax Expense (Benefit)		(5.7)	(5.2)	(4.5)
Current Income Tax Expense (Benefit)		(5.7)	(5.2)	(4.5)
Deferred Federal Income Tax Expense (Benefit)		126.0	98.8	160.0
Deferred State and Local Income Tax Expense (Benefit)		28.0	4.5	18.2
Deferred Income Tax Expense (Benefit)		154.0	103.3	178.2
Investment Tax Credit		(0.2)	(0.7)	(0.9)
Income Tax Expense (Benefit)		$ 148.1	$ 97.4	$ 172.8
Statutory Federal tax rate		35.00%	35.00%	35.00%
Federal renewable energy credit	[1]	(6.80%)	(8.90%)	(6.70%)
Remeasurement of state deferred tax liabilities		0.90%	(0.80%)	0.40%
401(k) dividends		(0.60%)	(0.70%)	(0.50%)
Federal investment tax credits, net		(0.80%)	(0.20%)	(0.20%)
State income taxes, net of Federal income tax benefit		1.90%	0.10%	1.20%
Uncertain tax positions		0.10%	0.70%	0.50%
Amortization of net unfunded deferred taxes		0.70%	0.90%	0.60%
Other		0.10%	0.30%	0.10%
Effective income tax rate		30.50%	26.40%	30.40%
Accrued liabilities		$ (16.1)	$ (14.0)
Accrued vacation		(3.5)	(3.2)
Uncollectible accounts		(0.6)	(0.5)
Accelerated depreciation and other property related differences		2,103.2	2,016.0
Investment in Enable Midstream Partners		657.3	623.4
Regulatory asset		34.4	32.7
Income taxes refundable to customers, net		24.1	22.0
Income taxes refundable to customers, net		16.5	13.7
Bond redemption-unamortized costs		4.3	4.8
Derivative instruments		2.2	1.5
Federal tax credits		(220.6)	(184.4)
State tax credits		(112.2)	(106.7)
Net operating losses		(31.7)	(94.6)
Accrued liabilities		(48.9)	(56.2)
Other		(34.6)	(46.3)
Asset retirement obligations		(24.5)	(22.5)
Deferred Federal investment tax credits		(0.8)	(0.9)
Other		(14.0)	(6.6)
Non-Current Deferred Income Tax Liabilities, net		2,334.5	2,178.2
Unrecognized Tax Benefits		20.7	20.2	$ 16.1	$ 12.0
Current year additions		0.5	4.1	4.1
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued		0.0
Unrecognized Tax Benefits, Period Increase (Decrease)		0.5
Tax Credit Carryforward, Deferred Tax Asset		220.6	184.4
Employee Service Share-based Compensation, Unrecognized Tax Benefit from Compensation Expense		24.8
State operating loss [Member]
Operating Loss Carryforwards		554.7
Deferred Tax Assets, Operating Loss Carryforwards, State and Local		$ 20.4
Tax Credit Carryforward, Expiration Date		Dec. 31, 2030
Federal operating loss [Member]
Operating Loss Carryforwards		$ 32.2
Net operating losses		$ 11.3
Tax Credit Carryforward, Expiration Date		Dec. 31, 2030
Federal tax credits [Member]
Federal tax credits		$ (220.6)
Tax Credit Carryforward, Amount		220.6
Tax Credit Carryforward, Deferred Tax Asset		$ 220.6
Tax Credit Carryforward, Expiration Date		Dec. 31, 2029
Oklahoma investment tax credits [Member]
Federal tax credits		$ (88.2)
Tax Credit Carryforward, Amount		135.7
Tax Credit Carryforward, Deferred Tax Asset		88.2
Oklahoma capital investment board credits [Member]
Federal tax credits		(7.3)
Tax Credit Carryforward, Amount		7.3
Tax Credit Carryforward, Deferred Tax Asset		7.3
Oklahoma zero emission tax credits [Member]
Federal tax credits		(16.2)
Tax Credit Carryforward, Amount		24.1
Tax Credit Carryforward, Deferred Tax Asset		$ 16.2
Tax Credit Carryforward, Expiration Date		Dec. 31, 2020
Louisiana inventory credits [Member] [Member] [Domain]
Federal tax credits		$ (0.5)
Tax Credit Carryforward, Amount		0.7
Tax Credit Carryforward, Deferred Tax Asset		$ 0.5
Tax Credit Carryforward, Expiration Date		Dec. 31, 2019
State and Local Jurisdiction [Member]
Unrecognized Tax Benefits, Period Increase (Decrease)		$ 0.3
OGE Energy Corp. [Member]
Unrecognized Tax Benefits		13.7
Og and E [Member]
Unrecognized Tax Benefits		$ 13.5	$ 13.2	$ 10.5

[1] Represents credits associated with the production from OG&E's wind farms.