EFFECTS OF REGULATION - Regulatory Asset - I&M (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2024
Regulatory Asset [Line Items]
Total Current Regulatory Assets	$ 514.0	$ 445.9
Total Noncurrent Regulatory Assets	5,092.4	5,129.2
Pending final regulatory approval
Regulatory Asset [Line Items]
Total Noncurrent Regulatory Assets	837.3	1,310.8
Approved for recovery
Regulatory Asset [Line Items]
Total Noncurrent Regulatory Assets	4,255.1	3,818.4
Earns/earning a return | Under-recovered Fuel Costs
Regulatory Asset [Line Items]
Total Current Regulatory Assets	357.4	$ 245.7
Remaining Recovery Period		1 year
Earns/earning a return | Pending final regulatory approval
Regulatory Asset [Line Items]
Total Noncurrent Regulatory Assets	349.9	$ 395.1
Earns/earning a return | Pending final regulatory approval | Other Regulatory Assets Pending Final Regulatory Approval
Regulatory Asset [Line Items]
Total Noncurrent Regulatory Assets	49.8	20.7
Earns/earning a return | Pending final regulatory approval | Storm-Related Costs
Regulatory Asset [Line Items]
Total Noncurrent Regulatory Assets	0.0	51.0
Earns/earning a return | Approved for recovery
Regulatory Asset [Line Items]
Total Noncurrent Regulatory Assets	1,946.9	$ 1,711.5
Earns/earning a return | Approved for recovery | Plant Retirement Costs - Asset Retirement Obligation Costs
Regulatory Asset [Line Items]
Remaining Recovery Period		16 years
Total Noncurrent Regulatory Assets	110.8	$ 111.0
Earns/earning a return | Approved for recovery | Storm-Related Costs
Regulatory Asset [Line Items]
Remaining Recovery Period		7 years
Total Noncurrent Regulatory Assets	170.9	$ 106.7
Earns/earning a return | Approved for recovery | Plant Retirement Costs - Unrecovered Plant
Regulatory Asset [Line Items]
Remaining Recovery Period		22 years
Total Noncurrent Regulatory Assets	664.2	$ 661.2
Earns/earning a return | Approved for recovery | Rockport Plant Dry Sorbent Injection System and Selective Catalytic Reduction
Regulatory Asset [Line Items]
Remaining Recovery Period		4 years
Total Noncurrent Regulatory Assets	46.9	$ 37.3
Earns/earning a return | Approved for recovery | Other Regulatory Assets Approved for Recovery
Regulatory Asset [Line Items]
Total Noncurrent Regulatory Assets	124.9	159.9
Does not earns/earning a return | Under-recovered Fuel Costs
Regulatory Asset [Line Items]
Total Current Regulatory Assets	62.7	$ 116.0
Remaining Recovery Period		1 year
Does not earns/earning a return | Pending final regulatory approval
Regulatory Asset [Line Items]
Total Noncurrent Regulatory Assets	487.4	$ 915.7
Does not earns/earning a return | Pending final regulatory approval | Other Regulatory Assets Pending Final Regulatory Approval
Regulatory Asset [Line Items]
Total Noncurrent Regulatory Assets	52.6	86.3
Does not earns/earning a return | Pending final regulatory approval | Plant Retirement Costs - Asset Retirement Obligation Costs
Regulatory Asset [Line Items]
Total Noncurrent Regulatory Assets	25.9	357.4
Does not earns/earning a return | Pending final regulatory approval | Storm-Related Costs
Regulatory Asset [Line Items]
Total Noncurrent Regulatory Assets	408.9	300.8
Does not earns/earning a return | Approved for recovery
Regulatory Asset [Line Items]
Total Noncurrent Regulatory Assets	2,308.2	$ 2,106.9
Does not earns/earning a return | Approved for recovery | Plant Retirement Costs - Asset Retirement Obligation Costs
Regulatory Asset [Line Items]
Remaining Recovery Period		18 years
Total Noncurrent Regulatory Assets	330.2	$ 360.1
Does not earns/earning a return | Approved for recovery | Storm-Related Costs
Regulatory Asset [Line Items]
Remaining Recovery Period		7 years
Total Noncurrent Regulatory Assets	38.5	$ 66.5
Does not earns/earning a return | Approved for recovery | Other Regulatory Assets Approved for Recovery
Regulatory Asset [Line Items]
Total Noncurrent Regulatory Assets	269.1	$ 240.1
Does not earns/earning a return | Approved for recovery | Cook Plant Nuclear Refueling Outage Levelization
Regulatory Asset [Line Items]
Remaining Recovery Period		3 years
Total Noncurrent Regulatory Assets	55.7	$ 43.0
Does not earns/earning a return | Approved for recovery | Pension and OPEB Funded Status
Regulatory Asset [Line Items]
Remaining Recovery Period		12 years
Total Noncurrent Regulatory Assets	1,054.1	$ 974.2
Does not earns/earning a return | Approved for recovery | Unamortized Loss on Reacquired Debt
Regulatory Asset [Line Items]
Remaining Recovery Period		24 years
Total Noncurrent Regulatory Assets	97.2	$ 90.9
Does not earns/earning a return | Approved for recovery | Postemployment Benefits
Regulatory Asset [Line Items]
Remaining Recovery Period		3 years
Total Noncurrent Regulatory Assets	30.6	$ 27.9
INDIANA MICHIGAN POWER COMPANY
Regulatory Asset [Line Items]
Total Current Regulatory Assets	14.8	10.6
Total Noncurrent Regulatory Assets	406.3	548.1
INDIANA MICHIGAN POWER COMPANY | Pending final regulatory approval
Regulatory Asset [Line Items]
Total Noncurrent Regulatory Assets	33.2	115.0
INDIANA MICHIGAN POWER COMPANY | Approved for recovery
Regulatory Asset [Line Items]
Total Noncurrent Regulatory Assets	373.1	433.1
INDIANA MICHIGAN POWER COMPANY | Earns/earning a return | Under-recovered Fuel Costs
Regulatory Asset [Line Items]
Total Current Regulatory Assets	14.8	$ 10.6
Remaining Recovery Period		1 year
INDIANA MICHIGAN POWER COMPANY | Earns/earning a return | Pending final regulatory approval
Regulatory Asset [Line Items]
Total Noncurrent Regulatory Assets	0.2	$ 6.4
INDIANA MICHIGAN POWER COMPANY | Earns/earning a return | Pending final regulatory approval | Other Regulatory Assets Pending Final Regulatory Approval
Regulatory Asset [Line Items]
Total Noncurrent Regulatory Assets	0.2	6.4
INDIANA MICHIGAN POWER COMPANY | Earns/earning a return | Approved for recovery
Regulatory Asset [Line Items]
Total Noncurrent Regulatory Assets	229.3	$ 194.8
INDIANA MICHIGAN POWER COMPANY | Earns/earning a return | Approved for recovery | Plant Retirement Costs - Unrecovered Plant
Regulatory Asset [Line Items]
Remaining Recovery Period		4 years
Total Noncurrent Regulatory Assets	122.5	$ 98.0
INDIANA MICHIGAN POWER COMPANY | Earns/earning a return | Approved for recovery | Rockport Plant Dry Sorbent Injection System and Selective Catalytic Reduction
Regulatory Asset [Line Items]
Remaining Recovery Period		4 years
Total Noncurrent Regulatory Assets	46.9	$ 37.3
INDIANA MICHIGAN POWER COMPANY | Earns/earning a return | Approved for recovery | Cook Plant Uprate Project
Regulatory Asset [Line Items]
Remaining Recovery Period		9 years
Total Noncurrent Regulatory Assets	22.9	$ 20.5
INDIANA MICHIGAN POWER COMPANY | Earns/earning a return | Approved for recovery | Deferred Cook Plant Life Cycle Management Project Costs - Michigan, FERC
Regulatory Asset [Line Items]
Remaining Recovery Period		10 years
Total Noncurrent Regulatory Assets	11.1	$ 10.1
INDIANA MICHIGAN POWER COMPANY | Earns/earning a return | Approved for recovery | Cook Plant Turbine - Indiana
Regulatory Asset [Line Items]
Remaining Recovery Period		14 years
Total Noncurrent Regulatory Assets	8.4	$ 7.8
INDIANA MICHIGAN POWER COMPANY | Earns/earning a return | Approved for recovery | Other Regulatory Assets Approved for Recovery
Regulatory Asset [Line Items]
Total Noncurrent Regulatory Assets	17.5	21.1
INDIANA MICHIGAN POWER COMPANY | Does not earns/earning a return | Pending final regulatory approval
Regulatory Asset [Line Items]
Total Noncurrent Regulatory Assets	33.0	108.6
INDIANA MICHIGAN POWER COMPANY | Does not earns/earning a return | Pending final regulatory approval | Other Regulatory Assets Pending Final Regulatory Approval
Regulatory Asset [Line Items]
Total Noncurrent Regulatory Assets	3.3	1.6
INDIANA MICHIGAN POWER COMPANY | Does not earns/earning a return | Pending final regulatory approval | Plant Retirement Costs - Asset Retirement Obligation Costs
Regulatory Asset [Line Items]
Total Noncurrent Regulatory Assets	0.0	74.0
INDIANA MICHIGAN POWER COMPANY | Does not earns/earning a return | Pending final regulatory approval | NOLC Costs - Indiana
Regulatory Asset [Line Items]
Total Noncurrent Regulatory Assets	0.0	26.7
INDIANA MICHIGAN POWER COMPANY | Does not earns/earning a return | Pending final regulatory approval | Storm-Related Costs
Regulatory Asset [Line Items]
Total Noncurrent Regulatory Assets	29.7	6.3
INDIANA MICHIGAN POWER COMPANY | Does not earns/earning a return | Approved for recovery
Regulatory Asset [Line Items]
Total Noncurrent Regulatory Assets	143.8	$ 238.3
INDIANA MICHIGAN POWER COMPANY | Does not earns/earning a return | Approved for recovery | Storm-Related Costs
Regulatory Asset [Line Items]
Remaining Recovery Period		4 years
Total Noncurrent Regulatory Assets	3.4	$ 20.2
INDIANA MICHIGAN POWER COMPANY | Does not earns/earning a return | Approved for recovery | Other Regulatory Assets Approved for Recovery
Regulatory Asset [Line Items]
Total Noncurrent Regulatory Assets	17.6	20.2
INDIANA MICHIGAN POWER COMPANY | Does not earns/earning a return | Approved for recovery | Income Taxes, Net
Regulatory Asset [Line Items]
Total Noncurrent Regulatory Assets	0.0	$ 108.8
Regulatory asset, not subject to rate normalization requirements, amount	$ 12.0
Regulatory asset, not subject to rate normalization requirements, refund period	4 years
INDIANA MICHIGAN POWER COMPANY | Does not earns/earning a return | Approved for recovery | Cook Plant Nuclear Refueling Outage Levelization
Regulatory Asset [Line Items]
Remaining Recovery Period		3 years
Total Noncurrent Regulatory Assets	$ 55.7	$ 43.0
INDIANA MICHIGAN POWER COMPANY | Does not earns/earning a return | Approved for recovery | Pension and OPEB Funded Status
Regulatory Asset [Line Items]
Remaining Recovery Period		12 years
Total Noncurrent Regulatory Assets	25.4	$ 14.6
INDIANA MICHIGAN POWER COMPANY | Does not earns/earning a return | Approved for recovery | Excess SO2 Allowance Inventory - Indiana
Regulatory Asset [Line Items]
Remaining Recovery Period		4 years
Total Noncurrent Regulatory Assets	14.8	$ 11.9
INDIANA MICHIGAN POWER COMPANY | Does not earns/earning a return | Approved for recovery | Unamortized Loss on Reacquired Debt
Regulatory Asset [Line Items]
Remaining Recovery Period		24 years
Total Noncurrent Regulatory Assets	11.8	$ 10.9
INDIANA MICHIGAN POWER COMPANY | Does not earns/earning a return | Approved for recovery | Postemployment Benefits
Regulatory Asset [Line Items]
Remaining Recovery Period		3 years
Total Noncurrent Regulatory Assets	7.0	$ 7.3
INDIANA MICHIGAN POWER COMPANY | Does not earns/earning a return | Approved for recovery | Environmental Cost Rider - Indiana
Regulatory Asset [Line Items]
Remaining Recovery Period		2 years
Total Noncurrent Regulatory Assets	$ 8.1	$ 1.4