Regulated Operations (Details) - USD ($) $ in Millions		Sep. 30, 2022	Dec. 31, 2021
Schedule of Regulatory Assets and Liabilities [Line Items]
Deferred Fuel Cost		$ 507.2	$ 151.9
Current Regulatory Assets		514.1	182.6
Non-Current Regulatory Assets		493.9	1,230.8
Current Regulatory Liabilities		12.0	2.5
Non-Current Regulatory Liabilities		1,178.7	1,231.1
OKLAHOMA
Schedule of Regulatory Assets and Liabilities [Line Items]
Deferred Fuel Cost		467.0	140.4
ARKANSAS
Schedule of Regulatory Assets and Liabilities [Line Items]
Deferred Fuel Cost		40.2	11.5
Other (B)
Schedule of Regulatory Assets and Liabilities [Line Items]
Current Regulatory Liabilities	[1]	1.5	2.5
Non-Current Regulatory Liabilities		2.0	3.6
Income taxes refundable to customers, net
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-Current Regulatory Liabilities		904.2	930.7
Accrued removal obligations, net
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-Current Regulatory Liabilities		272.5	296.8
Oklahoma investment tax credit rider
Schedule of Regulatory Assets and Liabilities [Line Items]
Current Regulatory Liabilities	[1]	5.3	0.0
Oklahoma EE Rider over recoveries
Schedule of Regulatory Assets and Liabilities [Line Items]
Current Regulatory Liabilities	[1]	5.2	0.0
Winter Storm Uri costs | OKLAHOMA
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-Current Regulatory Assets		0.0	747.9
Winter Storm Uri costs | ARKANSAS
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-Current Regulatory Assets		80.6	88.9
Benefit obligations regulatory asset
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-Current Regulatory Assets		99.1	109.2
Oklahoma deferred storm expenses
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-Current Regulatory Assets		203.3	172.8
Smart Grid
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-Current Regulatory Assets		0.3	3.9
Dry Scrubber Regulatory Asset [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-Current Regulatory Assets		18.3	18.9
Unamortized loss on reacquired debt
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-Current Regulatory Assets		8.3	8.9
Deferred Pension Expenses [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-Current Regulatory Assets		11.8	12.1
Other Regulatory Asset [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Current Regulatory Assets	[2]	6.7	9.7
Non-Current Regulatory Assets		11.0	10.4
Pension tracker
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-Current Regulatory Assets		47.6	42.9
SPP Cost Tracker Rider Under Recovery
Schedule of Regulatory Assets and Liabilities [Line Items]
Current Regulatory Assets	[2]	0.2	9.3
COVID-19 Deferred Expenses
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-Current Regulatory Assets		8.0	8.2
Oklahoma Energy Efficiency Rider Under Recovery
Schedule of Regulatory Assets and Liabilities [Line Items]
Current Regulatory Assets	[2]	0.0	11.7
Deferred Plant Expense
Schedule of Regulatory Assets and Liabilities [Line Items]
Non-Current Regulatory Assets		$ 5.6	$ 6.7

[1] Included in Other Current Liabilities in the condensed balance sheets.

[2] Included in Other Current Assets in the condensed balance sheets.