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Stock-Based Compensation (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
Stock-Based Compensation (Details) - USD ($) $ in Millions	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Stock-Based Compensation Activity
Income tax benefit	$ 0.6	$ 0.6	$ 1.2	$ 1.1
Treasury Stock, Shares, Acquired			154,344
OG&E [Member]
Stock-Based Compensation Activity
Income tax benefit	0.2	0.2	$ 0.3	0.4
Performance Shares [Member]
Stock-Based Compensation Activity
Compensation expense	1.9	2.1	3.9	4.0
Performance Shares [Member] \| Total Shareholder Return [Member]
Stock-Based Compensation Activity
Compensation expense	1.9	2.0	3.9	3.7
Performance Shares [Member] \| Performance Units Related to Earnings Per Share [Member]
Stock-Based Compensation Activity
Compensation expense	0.0	0.1	0.0	0.3
Performance Shares [Member] \| OG&E [Member]
Stock-Based Compensation Activity
Compensation expense	0.5	0.6	0.9	1.4
Performance Shares [Member] \| OG&E [Member] \| Total Shareholder Return [Member]
Stock-Based Compensation Activity
Compensation expense	0.5	0.6	0.9	1.3
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	0.2	0.9	0.3
Restricted stock units \| OG&E [Member]
Stock-Based Compensation Activity
Compensation expense	0.1	0.1	0.1	0.2
Share-based Payment Arrangement [Member]
Stock-Based Compensation Activity
Compensation expense	2.3	2.3	4.8	4.3
Share-based Payment Arrangement [Member] \| OG&E [Member]
Stock-Based Compensation Activity
Compensation expense	$ 0.6	$ 0.7	$ 1.0	$ 1.6