Rate Matters and Regulation (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2014
Additional Requested Plant Dismantlement Cost	$ 8.0
Change in Requested Return on Equity	0.25%
Change in Requested Rate Increase	$ 9.0
Oklahoma Attorney General [Member]
Reduction to Requested Additional Plant Dismantlement Costs	$ 20.9
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%
Oklahoma Public Utility Division Staff [Member]
Recommended Rate Increase (Decrease)	$ (6.1)
Recommended Return on Equity	9.25%
Recommended Common Equity Percentage	53.00%
Reduction to Requested Additional Plant Dismantlement Costs	$ 33.0
Oklahoma Industrial Electric Consumers [Member]
Recommended Rate Increase (Decrease)	$ 47.9
Recommended Return on Equity	9.00%
Recommended Common Equity Percentage	53.00%
Reduction to Requested Additional Plant Dismantlement Costs	$ 52.5
Administrative Law Judge [Member]
Recommended Return on Equity	9.87%
Recommended Increase (Decrease) in Revenue	$ 40.7
Recommended Capital Structure, Equity Percentage	53.00%
Recommended Capital Structure, Debt Percentage	47.00%
SmartHours Program [Member]
Lost Revenue Associated with Customer Programs - recovered annually	$ 10.1
Lost Revenue Associated with Customer Programs	30.3
Amount Recorded for Lost Revenue Associated with Customer Programs	36.6
Dry Scrubber Project [Member]
Estimated Environmental Capital Costs	547.5
Public Utilities, Property, Plant and Equipment, Construction Work in Progress	208.7
Mustang Modernization [Member]
Estimated Environmental Capital Costs	424.9
Public Utilities, Property, Plant and Equipment, Construction Work in Progress	187.8
OKLAHOMA
Public Utilities, Requested Rate Increase (Decrease), Amount	$ 92.5
Public Utilities, Requested Return on Equity, Percentage	10.25%
Public Utilities, Requested Equity Capital Structure, Percentage	53.00%
Investments Since Last Rate Case	$ 1,600.0
Public Utilities, Interim Rate Increase (Decrease), Amount	69.5
Interim Rate Collected	39.0
Interim Rate Revenue Reserved	33.7
ARKANSAS
Public Utilities, Requested Rate Increase (Decrease), Amount	$ 16.5
Public Utilities, Requested Return on Equity, Percentage	10.25%
Investments Since Last Rate Case	$ 3,000.0
Change in Allowed Amount [Member] | SmartHours Program [Member]
Lost Revenue Associated with Customer Programs	(6.3)
Recommendation 1 [Member] | Oklahoma Attorney General [Member]
Recommended Rate Increase (Decrease)	$ 10.8
Recommended Return on Equity	9.25%
Recommended Common Equity Percentage	50.00%
Recommendation 2 [Member] | Oklahoma Attorney General [Member]
Recommended Rate Increase (Decrease)	$ 13.7
Recommended Return on Equity	8.90%
Recommended Common Equity Percentage	53.00%
Public Utilities, Inventory, Fuel [Member]
Deferred Costs and Other Assets	$ 2.7	$ 11.0