Income Taxes (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016
Regulatory Liability, Noncurrent		$ 1,223.5	$ 1,270.7
Current Federal Tax Expense (Benefit)		(6.4)	(1.9)	$ 4.9
Current State and Local Tax Expense (Benefit)		5.1	(4.4)	(4.2)
Current Income Tax Expense (Benefit)		(1.3)	(6.3)	0.7
Deferred Federal Income Tax Expense (Benefit)		48.5	74.7	(75.9)
Deferred State and Local Income Tax Expense (Benefit)		(17.4)	3.7	26.0
Deferred Income Tax Expense (Benefit)		31.1	78.4	(49.9)
Investment Tax Credit		0.0	0.1	(0.1)
Income Tax Expense (Benefit)		$ 29.8	$ 72.2	$ (49.3)	[1]
Statutory federal tax rate		21.00%	21.00%	35.00%
Federal deferred tax revaluation		0.00%	0.40%	(41.20%)
Federal renewable energy credit (A)	[2]	(6.00%)	(5.10%)	(4.80%)
Remeasurement of state deferred tax liabilities		(0.80%)	(0.40%)	0.40%
401(k) dividends		(0.40%)	(0.30%)	(0.50%)
Federal investment tax credits, net		0.00%	0.00%	(0.10%)
State income taxes, net of federal income tax benefit		(1.20%)	0.40%	2.00%
Effective Income Tax Rate Reconciliation, Executive Compensation Limitation, Percent		0.20%	0.20%	0.00%
Amortization of net unfunded deferred taxes		(4.50%)	(2.10%)	0.70%
Other		(0.70%)	0.40%	(0.10%)
Effective income tax rate		6.40%	14.50%	(8.60%)
Accrued liabilities		$ (10.7)	$ (12.5)
Accrued vacation		(2.1)	(2.3)
Uncollectible accounts		(0.4)	(0.4)
Accelerated depreciation and other property related differences		1,656.8	1,605.3
Investment in Enable		478.2	469.9
Regulatory assets		28.4	17.4
Income taxes recoverable from customers, net		(229.9)	(239.6)
Company Pension Plan		4.1	7.6
Bond redemption-unamortized costs		2.2	2.4
Derivative instruments		1.6	1.7
Federal tax credits		(238.0)	(237.8)
State tax credits		(185.8)	(156.0)
Postretirement medical and life insurance benefits		(23.3)	(23.6)
Net operating losses		(16.6)	(20.2)
Regulatory liabilities		(68.1)	(78.8)
Asset retirement obligations		(19.2)	(21.5)
Deferred federal investment tax credits		(1.8)	(1.8)
Other		0.4	1.1
Total deferred income tax liabilities, net		1,375.8	1,310.9
Unrecognized Tax Benefits		20.7	20.7	$ 20.7		$ 20.7
Current year additions		0.0	0.0	$ 0.0
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued		0.0
Tax Credit Carryforward, Deferred Tax Asset		$ 238.0	$ 237.8
Stock-based compensation		(1.20%)	0.00%	0.00%
State operating loss [Member]
Operating Loss Carryforwards		$ 371.6
Deferred Tax Assets, Operating Loss Carryforwards, State and Local		16.6
Federal tax credits [Member]
Federal tax credits		(238.0)
Tax Credit Carryforward, Amount		238.0
Tax Credit Carryforward, Deferred Tax Asset		238.0
Oklahoma investment tax credits [Member]
State tax credits		(145.3)
Tax Credit Carryforward, Amount		183.9
Oklahoma capital investment board credits [Member]
State tax credits		(12.4)
Tax Credit Carryforward, Amount		12.4
Oklahoma zero emission tax credits [Member]
State tax credits		(28.0)
Tax Credit Carryforward, Amount		34.9
Louisiana inventory credits
State tax credits		(0.1)
Tax Credit Carryforward, Amount		0.2
Og and E [Member]
Unrecognized Tax Benefits		$ 16.4	$ 16.4	$ 16.4

[1] The Company recorded an income tax benefit of $245.2 million and income tax expense of $10.5 million during the fourth quarter of 2017 due to the Company remeasuring deferred taxes related to the natural gas midstream operations and other operations segments, respectively, as a result of the 2017 Tax Act.

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