Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended																12 Months Ended
	Dec. 31, 2018		Sep. 30, 2018		Jun. 30, 2018		Mar. 31, 2018		Dec. 31, 2017		Sep. 30, 2017		Jun. 30, 2017		Mar. 31, 2017		Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Operating revenues	$ 511.8		$ 698.8		$ 567.0		$ 492.7		$ 501.9		$ 716.8		$ 586.4		$ 456.0		$ 2,270.3		$ 2,261.1		$ 2,259.2
Operating income	58.0		227.3		137.7		66.6		85.7		249.1		147.3		49.8		489.6		531.9		530.8
Net income	$ 54.7		$ 205.1		$ 110.7		$ 55.0		$ 294.8		$ 183.4		$ 104.8		$ 36.0		$ 425.5		$ 619.0		$ 338.2
Basic earnings per average common share attributable to OGE Energy common shareholders	$ 0.27	[1]	$ 1.03	[1]	$ 0.55	[1]	$ 0.28	[1]	$ 1.48	[1]	$ 0.92	[1]	$ 0.52	[1]	$ 0.18	[1]	$ 2.13	[1]	$ 3.10	[1]	$ 1.69
Diluted earnings per average common share attributable to OGE Energy common shareholders	$ 0.27	[1]	$ 1.02	[1]	$ 0.55	[1]	$ 0.27	[1]	$ 1.48	[1]	$ 0.92	[1]	$ 0.52	[1]	$ 0.18	[1]	$ 2.12	[1]	$ 3.10	[1]	$ 1.69

[1] Due to the impact of dilution on the earnings per share calculation, quarterly earnings per share amounts may not add to the total.