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Common Equity Earnings Per Share (Details) - USD ($)
$ / shares in Units, shares in Millions, $ in Millions
 3 Months Ended 12 Months Ended
Dec. 31, 2017
Sep. 30, 2017
Jun. 30, 2017
Mar. 31, 2017
Dec. 31, 2016
Sep. 30, 2016
Jun. 30, 2016
Mar. 31, 2016
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount                 0.0 0.0 0.0
Net income attributable to OGE Energy $ 294.8 $ 183.4 $ 104.8 $ 36.0 $ 57.9 $ 183.6 $ 71.5 $ 25.2 $ 619.0 $ 338.2 $ 271.3
Basic Average Common Shares Outstanding                 199.7 199.7 199.6
Contingently Issuable Shares (Performance and Restricted Stock Units)                 0.3 0.2 0.0
Diluted Average Common Shares Outstanding                 200.0 199.9 199.6
Earnings Per Share, Basic and Diluted [Abstract]                      
Basic earnings per average common share attributable to OGE Energy common shareholders $ 1.48 [1] $ 0.92 [1] $ 0.52 [1] $ 0.18 [1] $ 0.29 [1] $ 0.92 [1] $ 0.35 [1] $ 0.13 [1] $ 3.10 [1] $ 1.69 [1] $ 1.36
Diluted earnings per average common share attributable to OGE Energy common shareholders $ 1.48 [1] $ 0.92 [1] $ 0.52 [1] $ 0.18 [1] $ 0.29 [1] $ 0.92 [1] $ 0.35 [1] $ 0.13 [1] $ 3.10 [1] $ 1.69 [1] $ 1.36
Retained Earnings [Member]                      
Net income attributable to OGE Energy                 $ 619.0 $ 338.2 $ 271.3
[1] Due to the impact of dilution on the earnings per share calculation, quarterly earnings per share amounts may not add to the total.