Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended																12 Months Ended
	Dec. 31, 2019		Sep. 30, 2019		Jun. 30, 2019		Mar. 31, 2019		Dec. 31, 2018		Sep. 30, 2018		Jun. 30, 2018		Mar. 31, 2018		Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
Operating revenues	$ 472.5		$ 755.4		$ 513.7		$ 490.0		$ 511.8		$ 698.8		$ 567.0		$ 492.7		$ 2,231.6		$ 2,270.3		$ 2,261.1
Operating income	70.3		274.3		110.0		49.7		58.0		227.3		137.7		66.6		504.3		489.6		531.9
Net income	$ 35.4		$ 250.9		$ 100.2		$ 47.1		$ 54.7		$ 205.1		$ 110.7		$ 55.0		$ 433.6		$ 425.5		$ 619.0
Basic earnings per average common share attributable to OGE Energy common shareholders	$ 0.18	[1]	$ 1.25	[1]	$ 0.50	[1]	$ 0.24	[1]	$ 0.27	[1]	$ 1.03	[1]	$ 0.55	[1]	$ 0.28	[1]	$ 2.17	[1]	$ 2.13	[1]	$ 3.10
Diluted earnings per average common share attributable to OGE Energy common shareholders	$ 0.18	[1]	$ 1.25	[1]	$ 0.50	[1]	$ 0.24	[1]	$ 0.27	[1]	$ 1.02	[1]	$ 0.55	[1]	$ 0.27	[1]	$ 2.16	[1]	$ 2.12	[1]	$ 3.10

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