Rate Matters and Regulation (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017
Public Utilities, Approved Rate Increase (Decrease), Amount		$ (64.0)
Public Utilities, Approved Return on Equity, Percentage		9.50%
Public Utilities, Approved Equity Capital Structure, Percentage		53.00%
Customer Refund Liability, Current		$ 0.3	$ 1.7
Interim Rate Revenue Reserved		$ 15.4
Public Utilities, Approved Debt Capital Structure, Percentage		47.00%
Regulatory Assets, Current		$ 18.5	40.8
Recommended Disallowance for Fuel Adjustment		3.3
Refund for Fuel Adjustment		2.4
Public Utilities, Amount Requested for Acquisition		$ 53.5
Oklahoma Corporation Commission [Member]
OG&E's Jurisdictional Revenues		86.00%
Arkansas Public Service Commission [Member]
OG&E's Jurisdictional Revenues		8.00%
Federal Energy Regulatory Commission [Member]
OG&E's Jurisdictional Revenues		6.00%
Dry Scrubber Project [Member]
Estimated Environmental Capital Costs		$ 520.0
Public Utilities, Property, Plant and Equipment, Construction Work in Progress		504.3
OKLAHOMA
Public Utilities, Requested Rate Increase (Decrease), Amount		77.6
Customer Refund Liability, Current		18.9
Interim Rate Revenue Reserved		5.6
ARKANSAS
Public Utilities, Requested Rate Increase (Decrease), Amount		6.4
Public Utilities, Approved Rate Increase (Decrease), Amount		(3.3)
Customer Refund Liability, Current		7.7
Oklahoma demand program rider under recovery [Member]
Regulatory Assets, Current	[1]	6.4	$ 31.6
January 16, 2018 [Member] | OKLAHOMA
Public Utilities, Requested Rate Increase (Decrease), Amount		$ 1.9
Public Utilities, Requested Return on Equity, Percentage		9.90%
FERC [Member]
Recommended Common Equity Percentage		7.85%
Public Utilities, Approved Return on Equity, Percentage		10.60%
Revenue impact of recommended change in return on common equity		$ 1.5

[1] Included in Other Current Assets on the Consolidated Balance Sheets.