Report of Business Segments (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Segment Reporting Information [Line Items]
Operating revenues	$ 743.9	$ 719.8	$ 1,728.4	$ 1,749.8
Cost of sales	269.8	259.8	645.4	682.3
Other operation and maintenance	113.1	109.4	354.6	334.3
Depreciation and amortization	82.2	77.9	240.8	230.0
Taxes other than income	21.5	21.9	66.5	68.8
OPERATING INCOME	257.3	250.8	421.1	434.4
Equity in earnings of unconsolidated affiliates	34.5	(71.9)	79.5	(12.0)
Other income	6.3	5.8	17.3	16.3
Interest expense	35.4	37.0	107.7	112.4
Income tax expense (benefit)	79.1	36.5	129.9	84.4
Net income	183.6	111.2	280.3	241.9
Investment in unconsolidated affiliates	1,168.0	1,202.2	1,168.0	1,202.2	$ 1,194.4
Total assets	9,784.0	9,600.7	9,784.0	9,600.7	$ 9,580.6
Electric Utility [Member]
Segment Reporting Information [Line Items]
Operating revenues	743.9	719.8	1,728.4	1,749.8
Cost of sales	269.8	259.8	645.4	682.3
Other operation and maintenance	115.2	107.4	356.3	337.3
Depreciation and amortization	80.8	75.9	235.9	224.0
Taxes other than income	20.9	21.0	63.6	65.7
OPERATING INCOME	257.2	255.7	427.2	440.5
Equity in earnings of unconsolidated affiliates	0.0	0.0	0.0	0.0
Other income	6.0	6.6	18.3	13.9
Interest expense	34.3	36.4	104.8	110.5
Income tax expense (benefit)	69.0	63.0	102.4	94.9
Net income	159.9	162.9	238.3	249.0
Investment in unconsolidated affiliates	0.0	0.0	0.0	0.0
Total assets	8,511.5	8,554.1	8,511.5	8,554.1
Natural Gas Midstream Operations [Member]
Segment Reporting Information [Line Items]
Operating revenues	0.0	0.0	0.0	0.0
Cost of sales	0.0	0.0	0.0	0.0
Other operation and maintenance	(0.1)	4.9	7.9	5.9
Depreciation and amortization	0.0	0.0	0.0	0.0
Taxes other than income	0.0	0.0	0.0	0.0
OPERATING INCOME	0.1	(4.9)	(7.9)	(5.9)
Equity in earnings of unconsolidated affiliates	34.5	(71.9)	79.5	(12.0)
Other income	0.0	0.0	0.0	0.0
Interest expense	0.0	0.0	0.0	0.0
Income tax expense (benefit)	12.1	(26.8)	31.5	(8.7)
Net income	22.5	(50.0)	40.1	(9.2)
Investment in unconsolidated affiliates	1,168.0	1,202.2	1,168.0	1,202.2
Total assets	1,503.1	1,541.5	1,503.1	1,541.5
Other Operations [Member]
Segment Reporting Information [Line Items]
Operating revenues	0.0	0.0	0.0	0.0
Cost of sales	0.0	0.0	0.0	0.0
Other operation and maintenance	(2.0)	(2.9)	(9.6)	(8.9)
Depreciation and amortization	1.4	2.0	4.9	6.0
Taxes other than income	0.6	0.9	2.9	3.1
OPERATING INCOME	0.0	0.0	1.8	(0.2)
Equity in earnings of unconsolidated affiliates	0.0	0.0	0.0	0.0
Other income	0.3	(0.7)	(0.8)	2.6
Interest expense	1.1	0.7	3.1	2.1
Income tax expense (benefit)	(2.0)	0.3	(4.0)	(1.8)
Net income	1.2	(1.7)	1.9	2.1
Investment in unconsolidated affiliates	0.0	0.0	0.0	0.0
Total assets	93.3	133.5	93.3	133.5
Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues	0.0	0.0	0.0	0.0
Cost of sales	0.0	0.0	0.0	0.0
Other operation and maintenance	0.0	0.0	0.0	0.0
Depreciation and amortization	0.0	0.0	0.0	0.0
Taxes other than income	0.0	0.0	0.0	0.0
OPERATING INCOME	0.0	0.0	0.0	0.0
Equity in earnings of unconsolidated affiliates	0.0	0.0	0.0	0.0
Other income	0.0	(0.1)	(0.2)	(0.2)
Interest expense	0.0	(0.1)	(0.2)	(0.2)
Income tax expense (benefit)	0.0	0.0	0.0	0.0
Net income	0.0	0.0	0.0	0.0
Investment in unconsolidated affiliates	0.0	0.0	0.0	0.0
Total assets	(323.9)	(628.4)	(323.9)	(628.4)
OGE Energy [Member]
Segment Reporting Information [Line Items]
Goodwill, Impairment Loss	$ 0.0	$ (177.7)	$ 0.6	(177.7)
Impairment Adjusted for Basis Difference [Member] | OGE Energy [Member]
Segment Reporting Information [Line Items]
Goodwill, Impairment Loss				$ 108.4