Retirement Plans and Postretirement Benefit Plans Postretirement Benefit Plans (Details) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
		Mar. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2020		Dec. 31, 2019
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Employer contributions		$ 40.0	$ 20.0	$ 20.0
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Level 3 Asset Value, Beginning of Period		33.4	34.8
Interest income			0.8
Dividend income			0.6
Unrealized gains			0.6
Realized losses			0.4
Administrative expenses and charges			(0.1)
Claims paid			(3.7)
Level 3 Asset Value, End of Period			$ 33.4	$ 34.8
Postretirement Plan, Expected Future Benefit Payments, Next Twelve Months						$ 11.9
Postretirement Plan, Expected Future Benefit Payments, Year Two						11.8
Postretirement Plan, Expected Future Benefit Payments, Year Three						11.4
Postretirement Plan, Expected Future Benefit Payments in Year Four						10.0
Postretirement Plan, Expected Future Benefit Payments, Year Five						9.5
Postretirement Plan, Expected Future Benefit Payments, Five Fiscal Years Thereafter						40.9
Postemployment Benefits Liability						$ 2.2		$ 2.1
Ultimate Health Care Cost Trend Rate						4.50%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Weighted-Average Interest Crediting Rate					4.00%	3.50%		4.00%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Weighted-Average Interest Crediting Rate			4.00%	4.00%	4.00%
Defined Contribution Plan, Cost			$ 18.2	$ 14.4	$ 13.2
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay			5.00%
Defined Contribution Plan, Employer Matching Contribution, Percent of Match			200.00%
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		33.4	$ 33.4	34.8		$ 33.4		$ 34.8
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Claims Paid			3.7
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Administrative Expenses and Charges			0.1
Unrealized gains			0.6
Interest income			0.8
Dividend income			0.6
Og and E [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Employer contributions			10.0	5.0
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Postretirement Plan, Expected Future Benefit Payments, Next Twelve Months						9.4
Postretirement Plan, Expected Future Benefit Payments, Year Two						9.3
Postretirement Plan, Expected Future Benefit Payments, Year Three						8.9
Postretirement Plan, Expected Future Benefit Payments in Year Four						7.7
Postretirement Plan, Expected Future Benefit Payments, Year Five						7.3
Postretirement Plan, Expected Future Benefit Payments, Five Fiscal Years Thereafter						31.0
Postemployment Benefits Liability						1.8		1.7
Defined Contribution Plan, Cost			14.3	11.0	9.8
Cash [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning			1.2
Fair Value of Plan Assets, Ending				1.2
Fair Value, Inputs, Level 1 [Member] | Cash [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning			1.2
Fair Value of Plan Assets, Ending				1.2
Fair Value, Inputs, Level 3 [Member] | Cash [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning			0.0
Fair Value of Plan Assets, Ending				0.0
Pension Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation, Beginning		654.6	616.1	615.9
Service cost			13.2	12.9	14.9
Interest cost			17.0	20.7	23.8
Plan settlements			(42.8)	(83.1)
Actuarial losses			57.7	64.3
Benefit Obligation, Ending			654.6	616.1	615.9
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		570.3	530.3	522.8
Actual return on plans' assets			77.0	85.2
Employer contributions			20.0	20.0
Plan settlements			(42.8)	(83.1)
Fair Value of Plan Assets, Ending			570.3	530.3	522.8
Funded Status of Plan						$ (84.3)		$ (85.8)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost			13.2	12.9	14.9
Interest cost			17.0	20.7	23.8
Expected return on plan assets			(37.6)	(36.1)	(44.1)
Amortization of unrecognized prior service cost	[1]		0.0	0.0	0.0
Curtailment			0.0	0.0	0.0
Settlement cost			14.1	27.6	25.1
Net periodic benefit cost			31.4	42.4	35.9
Amount paid by unconsolidated affiliates	[2]		2.0	2.9	2.5
Net Periodic Benefit Cost, Net of Unconsolidated Affiliates			29.4	39.5	33.4
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Capitalized Portion of Net Periodic Benefit Cost			$ 3.8	$ 3.6	$ 3.8
Assumptions Used Calculating Benefit Obligation, Discount Rate					4.20%	2.30%		3.15%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate			2.88%	3.63%	3.73%
Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets			7.50%	7.50%	7.50%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase					4.20%	4.20%		4.20%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase			4.20%	4.20%	4.20%
Defined Benefit Plan, Benefit Obligation, Benefits Paid			$ (14.2)	$ (14.6)
Defined Benefit Plan, Plan Assets, Benefits Paid			14.2	14.6
Accumulated Benefit Obligation						$ 610.8		$ 563.3
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment			0.0	0.0
Plan curtailments			0.0	0.0
Pension Plan [Member] | Og and E [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation, Beginning		484.1	462.0	453.6
Service cost			9.2	9.0	$ 9.8
Interest cost			12.6	15.6	17.6
Plan settlements			(33.5)	(45.6)
Actuarial losses			41.0	42.1
Benefit Obligation, Ending			484.1	462.0	453.6
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		420.3	399.1	387.6
Actual return on plans' assets			57.0	64.8
Employer contributions			10.0	5.0
Plan settlements			(33.5)	(45.6)
Fair Value of Plan Assets, Ending			420.3	399.1	387.6
Funded Status of Plan						(63.8)		(62.9)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost			9.2	9.0	9.8
Interest cost			12.6	15.6	17.6
Expected return on plan assets			(27.9)	(27.6)	(33.1)
Amortization of unrecognized prior service cost			0.0	0.0	0.0
Curtailment			0.0	0.0	0.0
Settlement cost			11.4	16.4	19.4
Net periodic benefit cost			22.5	26.3	25.8
Net Periodic Benefit Cost, Net of Unconsolidated Affiliates			28.4	30.8	31.5
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Capitalized Portion of Net Periodic Benefit Cost			3.1	3.0	3.2
Defined Benefit Plan, Benefit Obligation, Benefits Paid			(12.3)	(12.7)
Defined Benefit Plan, Plan Assets, Benefits Paid			12.3	12.7
Accumulated Benefit Obligation						454.7		425.8
Plan curtailments			0.0	0.0
Pension Plan [Member] | Equity Funds [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning	[3]	25.4	23.9
Fair Value of Plan Assets, Ending	[3]		25.4	23.9
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Alternative Investment						25.4	[4],[5]	23.9	[3],[6]
Pension Plan [Member] | Money market funds [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		8.8	2.4
Fair Value of Plan Assets, Ending			8.8	2.4
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Alternative Investment						$ 8.8	[4]	$ 2.4	[6]
Pension Plan [Member] | Total Plan assets [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		570.3	530.3
Fair Value of Plan Assets, Ending			570.3	530.3
Pension Plan [Member] | Total Plan assets [Member] | Og and E [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		420.3	399.1
Fair Value of Plan Assets, Ending			420.3	399.1
Pension Plan [Member] | Plan Assets Attributable to Affiliates
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		(150.0)	(131.2)
Fair Value of Plan Assets, Ending			(150.0)	(131.2)
Pension Plan [Member] | Fair Value, Inputs, Level 1 [Member] | Equity Funds [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning	[3]	0.0	0.0
Fair Value of Plan Assets, Ending	[3]		0.0	0.0
Pension Plan [Member] | Fair Value, Inputs, Level 1 [Member] | Money market funds [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		0.0	0.0
Fair Value of Plan Assets, Ending			0.0	0.0
Pension Plan [Member] | Fair Value, Inputs, Level 2 [Member] | Equity Funds [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning	[3]	0.0	0.0
Fair Value of Plan Assets, Ending	[3]		0.0	0.0
Pension Plan [Member] | Fair Value, Inputs, Level 2 [Member] | Money market funds [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		0.0	0.0
Fair Value of Plan Assets, Ending			0.0	0.0
Pension Plan [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		0.0	0.0
Fair Value of Plan Assets, Ending			0.0	0.0
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation, Beginning		144.5	136.5	135.8
Service cost			0.2	0.2	0.3
Interest cost			4.2	5.6	5.4
Actuarial losses			7.3	2.9
Benefit Obligation, Ending			144.5	136.5	135.8
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		47.6	47.0	45.3
Actual return on plans' assets			1.2	4.6
Employer contributions			7.1	5.1
Fair Value of Plan Assets, Ending			47.6	47.0	45.3
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost			0.2	0.2	0.3
Interest cost			4.2	5.6	5.4
Expected return on plan assets			(1.8)	(1.9)	(2.0)
Amortization of unrecognized prior service cost	[1]		(8.4)	(8.4)	(8.4)
Curtailment			(1.5)	0.0	0.0
Net periodic benefit cost			(2.3)	(2.5)	(0.9)
Amount paid by unconsolidated affiliates	[7]		(0.7)	(0.6)	(0.5)
Net Periodic Benefit Cost, Net of Unconsolidated Affiliates			(1.6)	(1.9)	(0.4)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Capitalized Portion of Net Periodic Benefit Cost			$ 0.2	$ 0.2	$ 0.2
Assumptions Used Calculating Benefit Obligation, Discount Rate					4.30%	2.45%		3.25%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate			3.25%	4.30%	3.70%
Health Care Cost Trend Rate Assumed for Next Fiscal Year						6.75%
Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets			4.00%	4.00%	4.00%
Defined Benefit Plan, Benefit Obligation, Benefits Paid			$ (11.0)	$ (12.1)
Defined Benefit Plan, Plan Assets, Benefits Paid			11.0	12.1
Accumulated Benefit Obligation						$ 96.9		$ 89.5
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment			0.0	0.0
Plan curtailments			4.0	0.0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Og and E [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation, Beginning		109.5	104.7	104.8
Service cost			0.2	0.2	$ 0.2
Interest cost			3.2	4.3	4.2
Actuarial losses			4.5	2.2
Benefit Obligation, Ending			109.5	104.7	104.8
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		42.7	41.9	40.6
Actual return on plans' assets			1.1	4.0
Employer contributions			5.9	4.1
Fair Value of Plan Assets, Ending			42.7	41.9	40.6
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost			0.2	0.2	0.2
Interest cost			3.2	4.3	4.2
Expected return on plan assets			(1.7)	(1.7)	(1.8)
Amortization of unrecognized prior service cost	[1]		(6.1)	(6.1)	(6.1)
Curtailment			(1.3)	0.0	0.0
Net periodic benefit cost			(1.0)	(1.2)	0.3
Net Periodic Benefit Cost, Net of Unconsolidated Affiliates			(1.5)	(1.8)	(0.4)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Capitalized Portion of Net Periodic Benefit Cost			0.1	0.1	0.1
Defined Benefit Plan, Benefit Obligation, Benefits Paid			(8.6)	(9.8)
Defined Benefit Plan, Plan Assets, Benefits Paid			8.6	9.8
Accumulated Benefit Obligation						66.8		62.8
Plan curtailments			3.1	0.0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Group Retiree Medical Insurance Contract [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		33.4	34.8
Fair Value of Plan Assets, Ending			33.4	34.8
Other Postretirement Benefit Plans, Defined Benefit [Member] | U.S. Equity Mutual Funds Investment [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		10.8	10.9
Fair Value of Plan Assets, Ending			10.8	10.9
Other Postretirement Benefit Plans, Defined Benefit [Member] | Cash [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		3.4
Fair Value of Plan Assets, Ending			3.4
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		14.2	12.1
Fair Value of Plan Assets, Ending			14.2	12.1
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | Group Retiree Medical Insurance Contract [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		0.0	0.0
Fair Value of Plan Assets, Ending			0.0	0.0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | U.S. Equity Mutual Funds Investment [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		10.8	10.9
Fair Value of Plan Assets, Ending			10.8	10.9
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | Cash [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		3.4
Fair Value of Plan Assets, Ending			3.4
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		0.0	0.0
Fair Value of Plan Assets, Ending			0.0	0.0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		33.4	34.8
Fair Value of Plan Assets, Ending			33.4	34.8
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Group Retiree Medical Insurance Contract [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		33.4	34.8
Fair Value of Plan Assets, Ending			33.4	34.8
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | U.S. Equity Mutual Funds Investment [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		0.0	0.0
Fair Value of Plan Assets, Ending			0.0	0.0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Cash [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		0.0
Fair Value of Plan Assets, Ending			0.0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		47.6	46.9
Fair Value of Plan Assets, Ending			47.6	46.9
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member] | Og and E [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		42.7	41.9
Fair Value of Plan Assets, Ending			42.7	41.9
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member] | OGE Energy [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		(4.9)	(5.0)
Fair Value of Plan Assets, Ending			(4.9)	(5.0)
Other Pension Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation, Beginning		7.8	10.3	9.6
Service cost			0.8	0.5	0.4
Interest cost			0.2	0.4	0.3
Plan settlements			(5.3)	(1.2)
Actuarial losses			1.6	0.7
Benefit Obligation, Ending			7.8	10.3	9.6
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		0.0	0.0	0.0
Actual return on plans' assets			0.0	0.0
Employer contributions			5.3	1.2
Plan settlements			(5.3)	(1.2)
Fair Value of Plan Assets, Ending			0.0	0.0	0.0
Funded Status of Plan						(7.8)		(10.3)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost			0.8	0.5	0.4
Interest cost			0.2	0.4	0.3
Expected return on plan assets			0.0	0.0	0.0
Amortization of unrecognized prior service cost	[1]		0.0	0.0	0.1
Curtailment			0.2	0.0	0.0
Settlement cost			2.7	0.5	1.0
Net periodic benefit cost			4.4	1.9	2.5
Amount paid by unconsolidated affiliates	[2]		0.1	0.1	0.1
Net Periodic Benefit Cost, Net of Unconsolidated Affiliates			4.3	1.8	2.4
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Defined Benefit Plan, Benefit Obligation, Benefits Paid			0.0	0.0
Defined Benefit Plan, Plan Assets, Benefits Paid			0.0	0.0
Accumulated Benefit Obligation						6.9		8.1
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment			0.0	0.3
Plan curtailments			0.2	0.0
Other Pension Plan [Member] | Og and E [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation, Beginning		3.0	6.1	6.0
Service cost			0.1	0.2	0.2
Interest cost			0.1	0.2	0.2
Plan settlements			(4.5)	(0.9)
Actuarial losses			1.2	0.6
Benefit Obligation, Ending			3.0	6.1	6.0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		$ 0.0	0.0	0.0
Actual return on plans' assets			0.0	0.0
Employer contributions			4.5	0.9
Plan settlements			(4.5)	(0.9)
Fair Value of Plan Assets, Ending			0.0	0.0	0.0
Funded Status of Plan						(3.0)		(6.1)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost			0.1	0.2	0.2
Interest cost			0.1	0.2	0.2
Expected return on plan assets			0.0	0.0	0.0
Amortization of unrecognized prior service cost			0.0	0.0	0.0
Curtailment			0.0	0.0	0.0
Settlement cost			2.4	0.5	0.4
Net periodic benefit cost			3.0	1.2	1.3
Net Periodic Benefit Cost, Net of Unconsolidated Affiliates			4.3	1.7	2.5
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Defined Benefit Plan, Benefit Obligation, Benefits Paid			0.0	0.0
Defined Benefit Plan, Plan Assets, Benefits Paid			0.0	0.0
Accumulated Benefit Obligation						$ 2.9		$ 4.8
Plan curtailments			0.0	0.0
OKLAHOMA | Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Settlement cost	[8]		21.6	17.9	22.1
OKLAHOMA | Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Settlement cost			$ 1.4	$ 0.0	$ 0.0

[1] Unamortized prior service cost is amortized on a straight-line basis over the average remaining service period to the first eligibility age of participants who are expected to receive a benefit and are active at the date of the plan amendment.

[2] Amount paid by unconsolidated affiliates" is only applicable to OGE Energy. "Amount allocated from OGE Energy" is only applicable to OG&E.

[3] This category represents units of participation in a commingled fund that primarily invested in stocks of international companies and emerging markets.

[4] GAAP allows the measurement of certain investments that do not have a readily determinable fair value at the net asset value. These investments do not consider the observability of inputs; therefore, they are not included within the fair value hierarchy.

[5] This category represents units of participation in a commingled fund that primarily invested in stocks of international companies and emerging markets.

[6] GAAP allows the measurement of certain investments that do not have a readily determinable fair value at the net asset value. These investments do not consider the observability of inputs; therefore, they are not included within the fair value hierarchy.

[7] "Amount paid by unconsolidated affiliates" is only applicable to OGE Energy. "Amount allocated from OGE Energy" is only applicable to OG&E.

[8] Included in the pension regulatory asset or liability in each jurisdiction, as indicated in the regulatory assets and liabilities table in Note 1.