Rate Matters and Regulation Rate Matters and Regulation (Details) $ in Millions	9 Months Ended
	Sep. 30, 2019 USD ($)
Public Utilities, Requested Rate Increase (Decrease), Amount	$ 5.9
Public Utilities, Amount Requested for Acquisition	53.5
Estimated Refund to SPP	13.0
OKLAHOMA
Public Utilities, Requested Rate Increase (Decrease), Amount	77.6
ARKANSAS
Public Utilities, Approved Rate Increase (Decrease), Amount	$ 3.3
FERC [Member]
Public Utilities, Approved Return on Equity, Percentage	10.60%
Recommended Common Equity Percentage	7.85%
Impact to Company [Member]
Estimated Refund to SPP	$ 5.0
Customer Impact [Member]
Estimated Refund to SPP	$ 8.0