Stock-Based Compensation (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020
Stock-Based Compensation Activity
Income tax benefit	$ 0.6	$ 0.5
Treasury Stock, Shares, Acquired	153,964
OG&E [Member]
Stock-Based Compensation Activity
Income tax benefit	$ 0.1	0.2
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted	249,909
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 38.06
Stock-Based Compensation Activity
Compensation expense	$ 2.0	1.9
Performance Shares [Member] \| OG&E [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted	68,720
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 38.14
Stock-Based Compensation Activity
Compensation expense	$ 0.4	0.8
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted	86,963
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 31.03
Stock-Based Compensation Activity
Compensation expense	$ 0.5	0.1
Restricted stock units \| OG&E [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted	22,911
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 30.91
Stock-Based Compensation Activity
Compensation expense	$ 0.0	0.1
Share-based Payment Arrangement [Member]
Stock-Based Compensation Activity
Compensation expense	2.5	2.0
Share-based Payment Arrangement [Member] \| OG&E [Member]
Stock-Based Compensation Activity
Compensation expense	0.4	0.9
Total Shareholder Return [Member] \| Performance Shares [Member]
Stock-Based Compensation Activity
Compensation expense	2.0	1.7
Total Shareholder Return [Member] \| Performance Shares [Member] \| OG&E [Member]
Stock-Based Compensation Activity
Compensation expense	0.4	0.7
Performance Units Related to Earnings Per Share [Member] \| Performance Shares [Member]
Stock-Based Compensation Activity
Compensation expense	0.0	0.2
Performance Units Related to Earnings Per Share [Member] \| Performance Shares [Member] \| OG&E [Member]
Stock-Based Compensation Activity
Compensation expense	$ 0.0	$ 0.1

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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Amount of tax benefit for recognition of expense of award under share-based payment arrangement.

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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