Report of Business Segments (Details) - USD ($) $ in Millions		3 Months Ended						9 Months Ended
		Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020		Dec. 31, 2020
Segment Reporting Information [Line Items]
Operating revenues		$ 864.4			$ 702.1			$ 3,072.4	$ 1,636.9
Fuel, purchased power and direct transmission expense		330.1			209.1			1,876.9	481.5
Other operation and maintenance		115.4			109.7			343.9	347.2
Depreciation and amortization		108.6			100.5			310.2	292.2
Taxes other than income		25.5			24.8			78.5	76.3
OPERATING INCOME		284.8			258.0			462.9	439.7
Equity in earnings of unconsolidated affiliates	[1]	41.2			15.8			127.9	(703.8)	[2]
Other Nonoperating Income (Expense)		2.1			(0.8)			2.9	3.3
Interest expense		39.5			39.8			118.8	118.9
Income Tax Expense (Benefit)		36.1			55.8			56.8	(151.2)
Net income (loss)		252.5	$ 112.9	$ 52.7	177.4	$ 85.9	$ (491.8)	418.1	(228.5)
Investment in unconsolidated affiliates		478.9			376.8			478.9	376.8		$ 397.4
Total assets		12,177.5			10,497.6			12,177.5	10,497.6		$ 10,718.8
Asset Impairment Charges	[3]	0.0			0.0			0.0	780.0
Electric Utility [Member]
Segment Reporting Information [Line Items]
Operating revenues		864.4			702.1			3,072.4	1,636.9
Fuel, purchased power and direct transmission expense		330.1			209.1			1,876.9	481.5
Other operation and maintenance		115.8			110.1			344.4	348.8
Depreciation and amortization		108.6			100.5			310.2	292.2
Taxes other than income		24.6			23.9			75.3	72.8
OPERATING INCOME		285.3			258.5			465.6	441.6
Equity in earnings of unconsolidated affiliates		0.0			0.0			0.0	0.0	[2]
Other Nonoperating Income (Expense)		2.9			0.6			5.8	2.9
Interest expense		38.0			39.5			114.3	115.7
Income Tax Expense (Benefit)		26.4			20.1			37.0	30.5
Net income (loss)		223.8			199.5			320.1	298.3
Investment in unconsolidated affiliates		0.0			0.0			0.0	0.0
Total assets		11,597.9			10,323.3			11,597.9	10,323.3
Natural Gas Midstream Operations [Member]
Segment Reporting Information [Line Items]
Operating revenues		0.0			0.0			0.0	0.0
Fuel, purchased power and direct transmission expense		0.0			0.0			0.0	0.0
Other operation and maintenance		0.3			0.3			2.3	1.2
Depreciation and amortization		0.0			0.0			0.0	0.0
Taxes other than income		0.1			0.2			0.3	0.4
OPERATING INCOME		(0.4)			(0.5)			(2.6)	(1.6)
Equity in earnings of unconsolidated affiliates		41.2			15.8			127.9	(703.8)	[2]
Other Nonoperating Income (Expense)		(0.5)			(0.7)			(1.2)	(0.7)
Interest expense		0.0			0.0			0.0	0.0
Income Tax Expense (Benefit)		9.5			4.5			23.2	(167.2)
Net income (loss)		30.8			10.1			100.9	(538.9)
Investment in unconsolidated affiliates		449.5			355.8			449.5	355.8
Total assets		451.8			358.7			451.8	358.7
Other Operations [Member]
Segment Reporting Information [Line Items]
Operating revenues		0.0			0.0			0.0	0.0
Fuel, purchased power and direct transmission expense		0.0			0.0			0.0	0.0
Other operation and maintenance		(0.7)			(0.7)			(2.8)	(2.8)
Depreciation and amortization		0.0			0.0			0.0	0.0
Taxes other than income		0.8			0.7			2.9	3.1
OPERATING INCOME		(0.1)			0.0			(0.1)	(0.3)
Equity in earnings of unconsolidated affiliates		0.0			0.0			0.0	0.0	[2]
Other Nonoperating Income (Expense)		(0.2)			(0.5)			(0.8)	2.5
Interest expense		1.6			0.5			5.4	4.6
Income Tax Expense (Benefit)		0.2			31.2			(3.4)	(14.5)
Net income (loss)		(2.1)			(32.2)			(2.9)	12.1
Investment in unconsolidated affiliates		29.4			21.0			29.4	21.0
Total assets		293.3			109.6			293.3	109.6
Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues		0.0			0.0			0.0	0.0
Fuel, purchased power and direct transmission expense		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	[2]
Other Nonoperating Income (Expense)		(0.1)			(0.2)			(0.9)	(1.4)
Interest expense		(0.1)			(0.2)			(0.9)	(1.4)
Income Tax Expense (Benefit)		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		$ (165.5)			$ (294.0)			$ (165.5)	$ (294.0)

[1] For the three and nine months ended September 30, 2020, Enable recorded a $225.0 million impairment on its SESH equity method investment, which is included in their net loss for each period. Enable estimated the fair value of this equity method investment was below the carrying value at September 30, 2020 and concluded the decline in value was other than temporary due to the expiration of a transportation contract and the current status of renewal negotiations. The impairment ran through OGE Energy's portion of Enable net income (loss) and was offset by basis differences that flow through the amortization of basis difference and dilution recognition line item above.

[2] In 2020, OGE Energy recorded a $780.0 million impairment on its investment in Enable, as further discussed in Note 4

[3] Effective March 31, 2020, OGE Energy estimated the fair value of its investment in Enable was below the book value and concluded the decline in value was not temporary due to the severity of the decline and recent rapid deterioration, as well as the near term future outlook, of the midstream oil and gas industry. Accordingly, OGE Energy recorded a $780.0 million impairment on its investment in Enable in 2020. Further discussion can be found in OGE Energy's 2020 Form 10-K.(C) For the three and nine months ended September 30, 2020, Enable recorded a $225.0 million impairment on its SESH equity method investment, which is included in their net loss for each period. Enable estimated the fair value of this equity method investment was below the carrying value at September 30, 2020 and concluded the decline in value was other than temporary due to the expiration of a transportation contract and the current status of renewal negotiations. The impairment ran through OGE Energy's portion of Enable net income (loss) and was offset by basis differences that flow through the amortization of basis difference and dilution recognition line item above.