Summary of Significant Accounting Policies - Schedule of Regulatory Assets and Liabilities (Details) - USD ($) $ in Millions		Dec. 31, 2022	Dec. 31, 2021
Schedule of Regulatory Assets and Liabilities [Line Items]
Fuel clause under recoveries		$ 514.9	$ 151.9
Regulatory Assets, Current		527.3	182.6
Regulatory Assets, Noncurrent		524.3	1,230.8
Regulatory Liability, Current		5.5	2.5
Regulatory Liability, Noncurrent		1,147.1	1,231.1
OKLAHOMA
Schedule of Regulatory Assets and Liabilities [Line Items]
Fuel clause under recoveries		474.3	140.4
ARKANSAS
Schedule of Regulatory Assets and Liabilities [Line Items]
Fuel clause under recoveries		40.6	11.5
SPP cost tracker under recovery [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Liability, Current	[1]	3.0	0.0
Accrued removal obligations [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Liability, Noncurrent		250.5	296.8
Pension tracker [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Noncurrent		57.2	42.9
Other Regulatory Liabilities [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Liability, Current	[1]	2.5	2.5
Regulatory Liability, Noncurrent		1.9	3.6
Oklahoma Energy Efficiency Rider Under Recovery
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Current	[2]	7.7	11.7
Benefit obligations regulatory asset [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Noncurrent		119.7	109.2
Deferred storm expenses [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Noncurrent		206.3	172.8
Unamortized loss on reacquired debt [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Noncurrent		8.0	8.9
Deferred Pension Expenses [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Noncurrent		12.3	12.1
Dry Scrubber Regulatory Asset [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Noncurrent		18.1	18.9
Other Regulatory Assets [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Current	[2]	4.7	19.0
Regulatory Assets, Noncurrent		11.6	14.3
Income taxes recoverable from customers, net [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Liability, Noncurrent		894.7	930.7
Deferred Plant Expense
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Noncurrent		5.2	6.7
COVID-19 Deferred Expenses
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Noncurrent		7.7	8.2
Winter Storm Uri Costs | OKLAHOMA
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Noncurrent		0.0	747.9
Winter Storm Uri Costs | ARKANSAS
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Noncurrent		$ 78.2	$ 88.9

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

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