Report of Business Segments (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020		Dec. 31, 2020
Segment Reporting Information [Line Items]
Operating revenues	$ 1,630.6	$ 431.3
Cost of sales	1,346.8	135.0
Other operation and maintenance	109.3	120.0
Depreciation and amortization	98.7	94.4
Taxes other than income	27.2	25.6
OPERATING INCOME	48.6	56.3
Equity in earnings of unconsolidated affiliates	53.2	(746.5)	[1]
Other Nonoperating Income (Expense)	0.9	2.1
Interest expense	39.4	38.3
Income Tax Expense (Benefit)	10.6	(234.6)
Net income (loss)	52.7	(491.8)
Investment in unconsolidated affiliates	432.8	367.5		$ 397.4
Total assets	11,788.7	10,370.9		$ 10,718.8
Electric Utility [Member]
Segment Reporting Information [Line Items]
Operating revenues	1,630.6	431.3
Cost of sales	1,346.8	135.0
Other operation and maintenance	110.3	121.0
Depreciation and amortization	98.7	94.4
Taxes other than income	25.7	23.9
OPERATING INCOME	49.1	57.0
Equity in earnings of unconsolidated affiliates	0.0	0.0	[1]
Other Nonoperating Income (Expense)	1.7	1.8
Interest expense	38.4	36.9
Income Tax Expense (Benefit)	1.2	2.0
Net income (loss)	11.2	19.9
Investment in unconsolidated affiliates	0.0	0.0
Total assets	11,248.2	10,030.7
Natural Gas Midstream Operations [Member]
Segment Reporting Information [Line Items]
Operating revenues	0.0	0.0
Cost of sales	0.0	0.0
Other operation and maintenance	0.4	0.6
Depreciation and amortization	0.0	0.0
Taxes other than income	0.1	0.1
OPERATING INCOME	(0.5)	(0.7)
Equity in earnings of unconsolidated affiliates	53.2	(746.5)	[1]
Other Nonoperating Income (Expense)	(0.5)	0.0
Interest expense	0.0	0.0
Income Tax Expense (Benefit)	14.3	(179.2)
Net income (loss)	37.9	(568.0)
Investment in unconsolidated affiliates	409.2	348.0
Total assets	415.4	353.4
Other Operations [Member]
Segment Reporting Information [Line Items]
Operating revenues	0.0	0.0
Cost of sales	0.0	0.0
Other operation and maintenance	(1.4)	(1.6)
Depreciation and amortization	0.0	0.0
Taxes other than income	1.4	1.6
OPERATING INCOME	0.0	0.0
Equity in earnings of unconsolidated affiliates	0.0	0.0	[1]
Other Nonoperating Income (Expense)	(0.1)	1.3
Interest expense	1.2	2.4
Income Tax Expense (Benefit)	(4.9)	(57.4)
Net income (loss)	3.6	56.3
Investment in unconsolidated affiliates	23.6	19.5
Total assets	521.6	252.9
Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues	0.0	0.0
Cost of sales	0.0	0.0
Other operation and maintenance	0.0	0.0
Depreciation and amortization	0.0	0.0
Taxes other than income	0.0	0.0
OPERATING INCOME	0.0	0.0
Equity in earnings of unconsolidated affiliates	0.0	0.0	[1]
Other Nonoperating Income (Expense)	(0.2)	(1.0)
Interest expense	(0.2)	(1.0)
Income Tax Expense (Benefit)	0.0	0.0
Net income (loss)	0.0	0.0
Investment in unconsolidated affiliates	0.0	0.0
Total assets	$ (396.5)	$ (266.1)

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