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