CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020		Dec. 31, 2019	Dec. 31, 2018
CASH FLOWS FROM OPERATING ACTIVITIES
Net income (loss)		$ (173.7)		$ 433.6	$ 425.5
Adjustments to reconcile net income (loss) to net cash provided from operating activities:
Depreciation and amortization		391.3		355.0	321.6
Deferred income taxes and investment tax credits, net		(134.5)		27.6	78.5
Equity in (earnings) losses of unconsolidated affiliates	[1]	668.0	[2]	(113.9)	(152.8)
Distributions from unconsolidated affiliates		91.7		125.5	141.2
Allowance for equity funds used during construction		(4.8)		(4.5)	(23.8)
Stock-based compensation expense		9.8		13.9	13.4
Regulatory assets		112.0		47.1	10.8
Regulatory liabilities		(64.0)		(45.6)	(16.5)
Other assets		(9.2)		(3.8)	6.2
Other liabilities		(26.3)		19.2	1.0
Change in certain current assets and liabilities:
Accounts receivable and accrued unbilled revenues, net		3.1		18.8	19.8
Income taxes receivable		2.8		(1.0)	(4.1)
Fuel, materials and supplies inventories		(8.9)		4.2	27.3
Fuel recoveries		63.3		(33.0)	(3.4)
Other current assets		(16.8)		5.1	25.1
Accounts payable		59.8		(34.5)	29.7
Other current liabilities		(26.8)		(38.0)	73.2
Net cash provided from operating activities		712.8		681.5	951.1
CASH FLOWS FROM INVESTING ACTIVITIES
Capital expenditures (less allowance for equity funds used during construction)		(650.5)		(635.5)	(573.6)
Investment in unconsolidated affiliates		(4.4)		(7.7)	(2.5)
Return of capital - unconsolidated affiliates		0.0		18.5	0.0
Proceeds from sale of assets		0.0		0.0	0.1
Net cash used in investing activities		(654.9)		(624.7)	(576.0)
CASH FLOWS FROM FINANCING ACTIVITIES
Increase (decrease) in short-term debt		(17.0)		112.0	(168.4)
Proceeds from long-term debt		297.1		296.5	396.0
Payment of long-term debt		(0.1)		(250.1)	(250.1)
Dividends paid on common stock		(314.9)		(299.2)	(272.2)
Cash paid for employee equity-based compensation and expense of common stock		(7.1)		(10.3)	(0.5)
Other		(0.1)		0.0	0.0
Purchase of treasury stock		(14.7)		0.0	0.0
Net cash used in financing activities		(56.8)		(151.1)	(295.2)
NET CHANGE IN CASH AND CASH EQUIVALENTS		1.1		(94.3)	79.9
CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR		0.0		94.3	14.4
CASH AND CASH EQUIVALENTS AT END OF YEAR		1.1		0.0	94.3
Interest costs capitalized		1.9		2.8	11.7
Interest (net of interest capitalized)		153.4		152.2	153.8
Income taxes (net of income tax refunds)		3.9		5.5	2.8
Power plant long-term service agreement		6.8		28.9	(9.2)
Og and E [Member]
Adjustments to reconcile net income (loss) to net cash provided from operating activities:
Depreciation and amortization		391.3		355.0	321.6
Deferred income taxes and investment tax credits, net		40.9		20.4	56.6
Allowance for equity funds used during construction		(4.8)		(4.5)	(23.8)
Stock-based compensation expense		3.0		4.9	4.6
Regulatory assets		112.0		47.1	10.8
Regulatory liabilities		(64.0)		(45.6)	(16.5)
Other assets		(3.4)		3.8	1.9
Other liabilities		(24.3)		8.4	0.0
Change in certain current assets and liabilities:
Accounts receivable and accrued unbilled revenues, net		4.5		17.0	19.5
Fuel, materials and supplies inventories		(8.9)		4.2	27.3
Fuel recoveries		63.3		(33.0)	(3.4)
Other current assets		(17.3)		5.9	23.1
Accounts payable		64.8		(30.0)	19.0
Other current liabilities		(26.8)		(35.1)	72.5
Net cash provided from operating activities		640.4		573.8	804.0
CASH FLOWS FROM INVESTING ACTIVITIES
Capital expenditures (less allowance for equity funds used during construction)		(650.5)		(635.5)	(573.6)
Proceeds from sale of assets		0.0		0.0	0.1
Net cash used in investing activities		(650.5)		(635.5)	(573.5)
CASH FLOWS FROM FINANCING ACTIVITIES
Proceeds from long-term debt		297.1		296.5	396.0
Payment of long-term debt		(0.1)		(250.1)	(250.1)
Dividends paid on common stock		(325.0)		0.0	(185.0)
Net cash used in financing activities		10.1		61.7	(230.5)
NET CHANGE IN CASH AND CASH EQUIVALENTS		0.0		0.0	0.0
CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR		0.0		0.0	0.0
CASH AND CASH EQUIVALENTS AT END OF YEAR		0.0		0.0	0.0
Interest costs capitalized		1.9		2.8	11.7
Net Income (Loss) Attributable to Parent		339.4		350.2	328.0
Increase (Decrease) in Income Taxes Payable		(5.3)		(0.7)	(15.6)
Changes In Advances With Parent		38.1		15.3	(191.4)
Interest (net of interest capitalized)		150.2		144.6	149.7
Income taxes (net of income tax refunds)		(0.2)		1.3	0.9
Power plant long-term service agreement		$ 6.8		$ 28.9	$ (9.2)

[1] For the year ended December 31, 2020, Enable recorded a $225.0 million impairment on its SESH equity method investment. 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 and was offset by basis differences that flow through the amortization of basis difference and dilution recognition line item above.

[2] In March 2020, OGE Energy recorded a $780.0 million impairment on its investment in Enable, as further discussed in Notes 5 and 7.