EFFECTS OF REGULATION - Regulatory Liabilities - PSO (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	$ 8,344.0	$ 8,182.4
Pending final regulatory determination
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	322.0	207.9
Approved for payment
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	8,022.0	7,974.5
Does not pay/paying a return | Pending final regulatory determination
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	146.0	104.8
Does not pay/paying a return | Pending final regulatory determination | FERC 2021 Transmission Formula Rate Challenge Refunds
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	131.3	103.1
Does not pay/paying a return | Approved for payment
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	2,495.6	2,151.4
Does not pay/paying a return | Approved for payment | Deferred Investment Tax Credits
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	$ 65.1	154.5
Remaining Refund Period	29 years
Does not pay/paying a return | Approved for payment | Other Regulatory Liabilities Approved for Payment
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	$ 90.1	106.5
Pays/paying a return | Pending final regulatory determination
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	176.0	103.1
Pays/paying a return | Pending final regulatory determination | Income Taxes, Net
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	176.0	103.1
Pays/paying a return | Approved for payment
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	5,526.4	5,823.1
Pays/paying a return | Approved for payment | Asset Removal Costs
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	3,828.0	3,563.5
Pays/paying a return | Approved for payment | Income Taxes, Net
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	1,622.1	2,179.7
Regulatory liabilities, not subject to rate normalization requirements, amount	$ 192.0	228.0
Regulatory liabilities, not subject to rate normalization requirements, refund period	10 years
Pays/paying a return | Approved for payment | Other Regulatory Liabilities Approved for Payment
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	$ 40.4	35.0
PUBLIC SERVICE COMPANY OF OKLAHOMA
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	689.7	765.6
PUBLIC SERVICE COMPANY OF OKLAHOMA | Approved for payment
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	688.1	764.4
PUBLIC SERVICE COMPANY OF OKLAHOMA | Does not pay/paying a return | Pending final regulatory determination
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	1.6	1.2
PUBLIC SERVICE COMPANY OF OKLAHOMA | Does not pay/paying a return | Pending final regulatory determination | FERC 2021 Transmission Formula Rate Challenge Refunds
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	1.6	1.2
PUBLIC SERVICE COMPANY OF OKLAHOMA | Does not pay/paying a return | Approved for payment
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	46.5	51.2
PUBLIC SERVICE COMPANY OF OKLAHOMA | Does not pay/paying a return | Approved for payment | Deferred Investment Tax Credits
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	$ 46.2	47.2
Remaining Refund Period	12 years
PUBLIC SERVICE COMPANY OF OKLAHOMA | Does not pay/paying a return | Approved for payment | Other Regulatory Liabilities Approved for Payment
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	$ 0.3	4.0
PUBLIC SERVICE COMPANY OF OKLAHOMA | Pays/paying a return | Approved for payment
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	641.6	713.2
PUBLIC SERVICE COMPANY OF OKLAHOMA | Pays/paying a return | Approved for payment | Asset Removal Costs
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	323.6	317.5
PUBLIC SERVICE COMPANY OF OKLAHOMA | Pays/paying a return | Approved for payment | Income Taxes, Net
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	318.0	395.7
Regulatory liabilities, not subject to rate normalization requirements, amount	$ 46.0	$ 51.0
Regulatory liabilities, not subject to rate normalization requirements, refund period	10 years