Rate Matters and Regulation Rate Matters and Regulation (Details) $ in Millions	9 Months Ended
	Sep. 30, 2022 USD ($)
Public Utilities, Requested Rate Increase (Decrease), Amount	$ 30.0
Estimated Refund to SPP	13.0
Plan Investments for Customers	$ 28.0
Common Equity Percentage which ROE is based	53.37%
Requested Recovery of Capital Investment	$ 1,200.0
Securitization Authorization Requested	760.0
Securitization Authorization Granted	$ 750.0
Public Utilities, Approved Return on Equity, Percentage	9.50%
Increase (Decrease) in Regulatory Clause Revenue	$ 424.0
Grid Enhancement
Public Utilities, Requested Rate Increase (Decrease), Amount	6.0
Maximum [Member]
Lost Revenue on Plant Investments for Customers	58.0
Minimum [Member]
Lost Revenue on Plant Investments for Customers	17.4
In Favor Cooperatives
Plan Investments for Customers	11.7
In Favor Cooperatives | Maximum [Member]
Lost Revenues on Plant Investments for Customers	7.0
In Favor Cooperatives | Minimum [Member]
Lost Revenues on Plant Investments for Customers	4.1
OKLAHOMA
Public Utilities, Requested Rate Increase (Decrease), Amount	$ 163.5
Public Utilities, Requested Return on Equity, Percentage	10.20%
Common Equity Percentage which ROE is based	53.37%
ARKANSAS
Public Utilities, Requested Rate Increase (Decrease), Amount	$ 4.2
Public Utilities, Approved Rate Increase (Decrease), Amount	8.5
Impact to Company [Member]
Estimated Refund to SPP	5.0
Customer Impact [Member]
Estimated Refund to SPP	$ 8.0