Summary of Significant Accounting Policies Asset Retirement Obligation (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at January 1		$ 79.6	$ 73.5
Accretion expense		0.6	0.5
Revisions in estimated cash flows	[1]	0.0	5.8
Liabilities settled	[2]	0.0	(0.2)
Balance at December 31		$ 80.2	$ 79.6

[1] Assumptions changed related to the estimated timing and estimated cost of the removal of asbestos at OG&E's generating facilities.

[2] Asset retirement obligations were settled for asbestos removal at one of OG&E's generating facilities