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)		(7.9)	(12.4)	$ 26.3
Current State and Local Tax Expense (Benefit)		4.1	(4.1)	(4.3)
Current Income Tax Expense (Benefit)		(3.8)	(16.5)	22.0
Deferred Federal Income Tax Expense (Benefit)		37.7	53.7	100.0
Deferred State and Local Income Tax Expense (Benefit)		(13.8)	2.7	19.9
Deferred Income Tax Expense (Benefit)		23.9	56.4	119.9
Investment Tax Credit		0.0	0.1	(0.1)
Income Tax Expense (Benefit)		$ 20.1	$ 40.0	$ 141.8
Statutory federal tax rate		21.00%	21.00%	35.00%
Amortization of net unfunded deferred taxes		(5.60%)	(2.90%)	0.90%
State income taxes, net of federal income tax benefit		(1.80%)	(0.20%)	2.20%
Federal renewable energy credit	[1]	(7.60%)	(6.90%)	(6.10%)
Other		(0.60%)	(0.10%)	(0.30%)
Effective income tax rate		5.40%	10.90%	31.70%
Accelerated depreciation and other property related differences		$ 1,656.8	$ 1,605.3
OG&E Pension Plan		24.5	26.0
Regulatory assets		28.4	17.4
Income taxes recoverable from customers, net		(229.9)	(239.6)
Bond redemption-unamortized costs		2.2	2.4
Federal tax credits		(238.0)	(237.5)
State tax credits		(170.8)	(142.3)
Postretirement medical and life insurance benefits		(16.0)	(16.2)
Net operating losses		(5.7)	(10.0)
Other		(4.7)	(2.4)
Deferred federal investment tax credits		(4.3)	(6.1)
Accrued vacation		(1.6)	(1.7)
Uncollectible accounts		(0.4)	(0.4)
Total deferred income tax liabilities, net		951.4	892.7
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	237.5
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Asset Retirement Obligations		19.2	21.5
Non-Current Deferred Tax Assets, Regulatory Liabilities		68.1	78.8
Non-Current Deferred Tax Assets, Deferred Federal Investment Tax Credits		1.8	$ 1.9
State operating loss [Member]
Operating Loss Carryforwards		127.3
Deferred Tax Assets, Operating Loss Carryforwards, State and Local		5.7
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		130.4
Tax Credit Carryforward, Amount		165.1
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
OG&E [Member]
Unrecognized Tax Benefits that Would Impact Effective Tax Rate		$ 16.4		$ 16.4

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