Report of Business Segments (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2015		Sep. 30, 2014		Sep. 30, 2015		Sep. 30, 2014		Dec. 31, 2014
Segment Reporting Information [Line Items]
Operating revenues	$ 719.8		$ 754.7		$ 1,749.8		$ 1,926.9
Cost of sales	259.8		305.3		682.3		869.6
Other operation and maintenance	109.4		108.1		334.3		331.9
Depreciation and amortization	77.9		71.7		230.0		207.2
Taxes other than income	21.9		21.5		68.8		66.5
OPERATING INCOME	250.8		248.1		434.4		451.7
Equity in earnings of unconsolidated affiliates (A)	(71.9)	[1]	44.7	[1]	(12.0)	[2]	131.9	[2]
Other income (expense)	5.8		2.5		16.3		3.5
Interest expense	37.0		37.2		112.4		112.5
Income tax expense	36.5		70.8		84.4		137.2
Net income (loss)	111.2		187.3		241.9		337.4
Investment in unconsolidated affiliates	1,202.2		1,311.1		1,202.2		1,311.1		$ 1,318.2
Total assets	9,617.8		9,462.7		9,617.8		9,462.7		$ 9,527.8
Electric Utility [Member]
Segment Reporting Information [Line Items]
Operating revenues	719.8		754.7		1,749.8		1,926.9
Cost of sales	259.8		305.3		682.3		869.6
Other operation and maintenance	107.4		111.0		337.3		343.1
Depreciation and amortization	75.9		69.4		224.0		198.7
Taxes other than income	21.0		20.6		65.7		63.1
OPERATING INCOME	255.7		248.4		440.5		452.4
Equity in earnings of unconsolidated affiliates (A)	0.0	[1]	0.0	[1]	0.0	[2]	0.0	[2]
Other income (expense)	6.6		2.9		13.9		4.5
Interest expense	36.4		35.3		110.5		106.7
Income tax expense	63.0		58.7		94.9		95.3
Net income (loss)	162.9		157.3		249.0		254.9
Investment in unconsolidated affiliates	0.0		0.0		0.0		0.0
Total assets	8,570.7		8,003.1		8,570.7		8,003.1
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	4.9		0.3		5.9		0.7
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	(4.9)		(0.3)		(5.9)		(0.7)
Equity in earnings of unconsolidated affiliates (A)	(71.9)	[1]	44.7	[1]	(12.0)	[2]	131.9	[2]
Other income (expense)	0.0		0.0		0.0		0.0
Interest expense	0.0		0.0		0.0		0.0
Income tax expense	(26.8)		16.2		(8.7)		49.6
Net income (loss)	(50.0)		28.2		(9.2)		81.6
Investment in unconsolidated affiliates	1,202.2		1,311.1		1,202.2		1,311.1
Total assets	1,541.5		1,427.2		1,541.5		1,427.2
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	(2.9)		(3.2)		(8.9)		(11.9)
Depreciation and amortization	2.0		2.3		6.0		8.5
Taxes other than income	0.9		0.9		3.1		3.4
OPERATING INCOME	0.0		0.0		(0.2)		0.0
Equity in earnings of unconsolidated affiliates (A)	0.0	[1]	0.0	[1]	0.0	[2]	0.0	[2]
Other income (expense)	(0.7)		(0.3)		2.6		(0.8)
Interest expense	0.7		2.0		2.1		6.0
Income tax expense	0.3		(4.1)		(1.8)		(7.7)
Net income (loss)	(1.7)		1.8		2.1		0.9
Investment in unconsolidated affiliates	0.0		0.0		0.0		0.0
Total assets	134.0		204.1		134.0		204.1
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 (A)	0.0	[1]	0.0	[1]	0.0	[2]	0.0	[2]
Other income (expense)	(0.1)		(0.1)		(0.2)		(0.2)
Interest expense	(0.1)		(0.1)		(0.2)		(0.2)
Income tax expense	0.0		0.0		0.0		0.0
Net income (loss)	0.0		0.0		0.0		0.0
Investment in unconsolidated affiliates	0.0		0.0		0.0		0.0
Total assets	(628.4)		$ (171.7)		(628.4)		$ (171.7)
OGE Energy [Member]
Segment Reporting Information [Line Items]
Goodwill, Impairment Loss	$ 108.4				$ 108.4

[1] The Company recorded a $108.4 million pre-tax charge during the three months ended September 30, 2015 for its share of Enable's goodwill impairment, as adjusted for the basis differences. See Note 3 for further discussion of Enable's goodwill impairment.

[2] The Company recorded a $108.4 million pre-tax charge during the nine months ended September 30, 2015 for its share of Enable's goodwill impairment, as adjusted for the basis differences. See Note 3 of this Form 10-Q for further discussion of Enable's goodwill impairment.