EFFECTS OF REGULATION - Regulatory Liabilities - I&M (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Regulatory Liability [Line Items]
Total Current Regulatory Liabilities	$ 53.5	$ 26.5
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 | Over-recovered Fuel Costs
Regulatory Liability [Line Items]
Total Current Regulatory Liabilities	$ 31.9	23.2
Remaining Refund Period	1 year
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 | Over-recovered Fuel Costs
Regulatory Liability [Line Items]
Remaining Refund Period	8 years
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	$ 32.1	26.1
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
Does not pay/paying a return | Approved for payment | Excess Nuclear Decommissioning Funding
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	2,137.3	1,721.9
Does not pay/paying a return | Approved for payment | Spent Nuclear Fuel
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	$ 50.4	47.6
Does not pay/paying a return | Approved for payment | Demand Side Management
Regulatory Liability [Line Items]
Remaining Refund Period	2 years
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	$ 52.6	31.3
Does not pay/paying a return | Approved for payment | Deferred Investment Tax Credits
Regulatory Liability [Line Items]
Remaining Refund Period	29 years
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	$ 65.1	154.5
Pays/paying a return | Over-recovered Fuel Costs
Regulatory Liability [Line Items]
Total Current Regulatory Liabilities	$ 21.6	3.3
Remaining Refund Period	1 year
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 | 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
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 | Other Regulatory Liabilities Approved for Payment
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	40.4	35.0
INDIANA MICHIGAN POWER COMPANY
Regulatory Liability [Line Items]
Total Current Regulatory Liabilities	10.3	23.2
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	2,480.8	2,052.3
INDIANA MICHIGAN POWER COMPANY | Pending final regulatory determination
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	43.4	(80.2)
INDIANA MICHIGAN POWER COMPANY | Approved for payment
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	2,437.4	2,132.5
INDIANA MICHIGAN POWER COMPANY | Does not pay/paying a return | Over-recovered Fuel Costs
Regulatory Liability [Line Items]
Total Current Regulatory Liabilities	$ 10.3	23.2
Remaining Refund Period	1 year
INDIANA MICHIGAN POWER COMPANY | Does not pay/paying a return | Pending final regulatory determination
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	$ 43.4	22.8
INDIANA MICHIGAN POWER COMPANY | 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	28.9	22.8
INDIANA MICHIGAN POWER COMPANY | Does not pay/paying a return | Pending final regulatory determination | Cook Plant PTC Deferral - Michigan
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	14.5	0.0
INDIANA MICHIGAN POWER COMPANY | Does not pay/paying a return | Approved for payment
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	2,238.8	1,820.9
INDIANA MICHIGAN POWER COMPANY | 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	2.3	4.8
INDIANA MICHIGAN POWER COMPANY | Does not pay/paying a return | Approved for payment | Excess Nuclear Decommissioning Funding
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	2,137.3	1,721.9
INDIANA MICHIGAN POWER COMPANY | Does not pay/paying a return | Approved for payment | Spent Nuclear Fuel
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	$ 50.4	47.6
INDIANA MICHIGAN POWER COMPANY | Does not pay/paying a return | Approved for payment | Demand Side Management
Regulatory Liability [Line Items]
Remaining Refund Period	2 years
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	$ 33.0	16.7
INDIANA MICHIGAN POWER COMPANY | Does not pay/paying a return | Approved for payment | Deferred Investment Tax Credits
Regulatory Liability [Line Items]
Remaining Refund Period	26 years
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	$ 13.8	15.8
INDIANA MICHIGAN POWER COMPANY | Does not pay/paying a return | Approved for payment | PJM Costs and Off-system Sales Margin Sharing - Indiana
Regulatory Liability [Line Items]
Remaining Refund Period	1 year
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	$ 2.0	14.1
INDIANA MICHIGAN POWER COMPANY | Pays/paying a return | Pending final regulatory determination
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	0.0	(103.0)
INDIANA MICHIGAN POWER COMPANY | Pays/paying a return | Pending final regulatory determination | Income Taxes, Net
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	0.0	(103.0)
INDIANA MICHIGAN POWER COMPANY | Pays/paying a return | Approved for payment
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	198.6	311.6
INDIANA MICHIGAN POWER COMPANY | Pays/paying a return | Approved for payment | Income Taxes, Net
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	0.0	116.8
Regulatory liabilities, not subject to rate normalization requirements, amount		25.0
INDIANA MICHIGAN POWER COMPANY | Pays/paying a return | Approved for payment | Asset Removal Costs
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	$ 174.2	168.1
INDIANA MICHIGAN POWER COMPANY | Pays/paying a return | Approved for payment | Renewable Energy Surcharge - Michigan
Regulatory Liability [Line Items]
Remaining Refund Period	2 years
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	$ 24.3	26.6
INDIANA MICHIGAN POWER COMPANY | 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	$ 0.1	$ 0.1