Revenue from Contracts with Customers (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	[1]	$ 564.5	$ 492.0	$ 2,185.5	$ 912.4
Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers		178.5	202.8	746.7	369.7
Commercial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers		108.3	113.0	415.8	204.3
Industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers		37.5	44.7	184.2	86.2
Oilfield
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers		28.7	38.4	189.5	76.6
Public authorities and street light
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers		37.0	40.6	160.1	75.3
System sales revenues
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers		390.0	439.5	1,696.3	812.1
Provision for rate refund
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers		0.0	(1.0)	0.0	(1.6)
Integrated market
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers		128.3	8.5	430.4	15.7
Transmission
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers		36.7	39.8	73.0	74.0
Other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers		$ 9.5	$ 5.2	$ (14.2)	$ 12.2

[1] In February 2021, Winter Storm Uri resulted in record winter peak demand for electricity and extremely high natural gas and purchased power prices in OG&E's service territory. Operating revenues significantly increased due to increased fuel, purchased power and direct transmission expenses, which are recoverable from customers, as a result of Winter Storm Uri. For further discussion, see Note 15 and "Item 2. Management's Discussion and Analysis of Financial Condition and Results of Operation."