Revenue from Contracts with Customers (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2021	Mar. 31, 2020
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	[1]	$ 1,621.0	$ 420.4
Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers		568.2	166.9
Commercial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers		307.5	91.3
Industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers		146.7	41.5
Oilfield
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers		160.8	38.2
Public authorities and street light
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers		123.1	34.7
System sales revenues
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers		1,306.3	372.6
Provision for rate refund
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers		0.0	(0.6)
Integrated market
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers		302.1	7.2
Transmission
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers		36.3	34.2
Other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers		$ (23.7)	$ 7.0

[1] In February 2021, OG&E's service territory experienced an unprecedented, prolonged, cold spell that resulted in record winter peak demand for electricity and extremely high natural gas and purchased power prices. Operating revenues significantly increased due to increased cost of sales, which are recovered from customers, as a result of the February 2021 extreme cold weather event. For further discussion, see Note 15 and "Item 2. Management's Discussion and Analysis of Financial Condition and Results of Operation."