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Stock-Based Compensation (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
Stock-Based Compensation (Details) - USD ($) $ in Millions	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Stock-Based Compensation Activity
Income tax benefit	$ 0.6	$ 0.6	$ 1.8	$ 1.7
Treasury Stock, Shares, Acquired			154,523
OG&E [Member]
Stock-Based Compensation Activity
Income tax benefit	0.1	0.2	$ 0.4	0.6
Performance Shares [Member]
Stock-Based Compensation Activity
Compensation expense	1.9	2.1	5.8	6.1
Performance Shares [Member] \| Total Shareholder Return [Member]
Stock-Based Compensation Activity
Compensation expense	1.9	1.9	5.8	5.6
Performance Shares [Member] \| Performance Units Related to Earnings Per Share [Member]
Stock-Based Compensation Activity
Compensation expense	0.0	0.2	0.0	0.5
Performance Shares [Member] \| OG&E [Member]
Stock-Based Compensation Activity
Compensation expense	0.5	0.5	1.4	1.9
Performance Shares [Member] \| OG&E [Member] \| Total Shareholder Return [Member]
Stock-Based Compensation Activity
Compensation expense	0.5	0.5	1.4	1.8
Performance Shares [Member] \| OG&E [Member] \| Performance Units Related to Earnings Per Share [Member]
Stock-Based Compensation Activity
Compensation expense	0.0	0.0	0.0	0.1
Restricted stock units
Stock-Based Compensation Activity
Compensation expense	0.4	0.3	1.3	0.6
Restricted stock units \| OG&E [Member]
Stock-Based Compensation Activity
Compensation expense	0.1	0.1	0.2	0.3
Share-based Payment Arrangement [Member]
Stock-Based Compensation Activity
Compensation expense	2.3	2.4	7.1	6.7
Share-based Payment Arrangement [Member] \| OG&E [Member]
Stock-Based Compensation Activity
Compensation expense	$ 0.6	$ 0.6	$ 1.6	$ 2.2