EFFECTS OF REGULATION - Regulatory Assets - I&M (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2025
Regulatory Asset [Line Items]
Total Current Regulatory Assets	$ 446	$ 426
Total Noncurrent Regulatory Assets	5,129	4,804
Pending final regulatory approval
Regulatory Asset [Line Items]
Total Noncurrent Regulatory Assets	1,311	1,307
Approved for recovery
Regulatory Asset [Line Items]
Total Noncurrent Regulatory Assets	3,818	3,497
Earns/earning a return | Under-recovered Fuel Costs
Regulatory Asset [Line Items]
Total Current Regulatory Assets	246	$ 140
Remaining Recovery Period		1 year
Earns/earning a return | Pending final regulatory approval
Regulatory Asset [Line Items]
Total Noncurrent Regulatory Assets	395	$ 435
Earns/earning a return | Pending final regulatory approval | Other Regulatory Assets Pending Final Regulatory Approval
Regulatory Asset [Line Items]
Total Noncurrent Regulatory Assets	21	23
Earns/earning a return | Pending final regulatory approval | Storm-Related Costs
Regulatory Asset [Line Items]
Total Noncurrent Regulatory Assets	51	43
Earns/earning a return | Approved for recovery
Regulatory Asset [Line Items]
Total Noncurrent Regulatory Assets	1,711	$ 1,341
Earns/earning a return | Approved for recovery | Plant Retirement Costs - Asset Retirement Obligation Costs
Regulatory Asset [Line Items]
Remaining Recovery Period		15 years
Total Noncurrent Regulatory Assets	111	$ 1
Earns/earning a return | Approved for recovery | Storm-Related Costs
Regulatory Asset [Line Items]
Remaining Recovery Period		6 years
Total Noncurrent Regulatory Assets	107	$ 100
Earns/earning a return | Approved for recovery | Plant Retirement Costs - Unrecovered Plant
Regulatory Asset [Line Items]
Remaining Recovery Period		21 years
Total Noncurrent Regulatory Assets	661	$ 470
Earns/earning a return | Approved for recovery | Rockport Plant Dry Sorbent Injection System and Selective Catalytic Reduction
Regulatory Asset [Line Items]
Remaining Recovery Period		3 years
Total Noncurrent Regulatory Assets	37	$ 28
Earns/earning a return | Approved for recovery | Other Regulatory Assets Approved for Recovery
Regulatory Asset [Line Items]
Total Noncurrent Regulatory Assets	204	199
Does not earns/earning a return | Under-recovered Fuel Costs
Regulatory Asset [Line Items]
Total Current Regulatory Assets	116	$ 202
Remaining Recovery Period		1 year
Does not earns/earning a return | Pending final regulatory approval
Regulatory Asset [Line Items]
Total Noncurrent Regulatory Assets	916	$ 872
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	87	163
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	357	257
Does not earns/earning a return | Pending final regulatory approval | Storm-Related Costs
Regulatory Asset [Line Items]
Total Noncurrent Regulatory Assets	301	191
Does not earns/earning a return | Approved for recovery
Regulatory Asset [Line Items]
Total Noncurrent Regulatory Assets	2,107	$ 2,156
Does not earns/earning a return | Approved for recovery | Plant Retirement Costs - Asset Retirement Obligation Costs
Regulatory Asset [Line Items]
Remaining Recovery Period		17 years
Total Noncurrent Regulatory Assets	360	$ 459
Does not earns/earning a return | Approved for recovery | Storm-Related Costs
Regulatory Asset [Line Items]
Remaining Recovery Period		6 years
Total Noncurrent Regulatory Assets	67	$ 158
Does not earns/earning a return | Approved for recovery | Other Regulatory Assets Approved for Recovery
Regulatory Asset [Line Items]
Total Noncurrent Regulatory Assets	229	$ 222
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	43	$ 82
INDIANA MICHIGAN POWER COMPANY
Regulatory Asset [Line Items]
Total Current Regulatory Assets	11	0
Total Noncurrent Regulatory Assets	548	585
INDIANA MICHIGAN POWER COMPANY | Pending final regulatory approval
Regulatory Asset [Line Items]
Total Noncurrent Regulatory Assets	115	118
INDIANA MICHIGAN POWER COMPANY | Approved for recovery
Regulatory Asset [Line Items]
Total Noncurrent Regulatory Assets	433	467
INDIANA MICHIGAN POWER COMPANY | Earns/earning a return | Under-recovered Fuel Costs
Regulatory Asset [Line Items]
Total Current Regulatory Assets	11	$ 0
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	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	6	4
INDIANA MICHIGAN POWER COMPANY | Earns/earning a return | Approved for recovery
Regulatory Asset [Line Items]
Total Noncurrent Regulatory Assets	195	$ 157
INDIANA MICHIGAN POWER COMPANY | Earns/earning a return | Approved for recovery | Plant Retirement Costs - Unrecovered Plant
Regulatory Asset [Line Items]
Remaining Recovery Period		3 years
Total Noncurrent Regulatory Assets	98	$ 73
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		3 years
Total Noncurrent Regulatory Assets	37	$ 28
INDIANA MICHIGAN POWER COMPANY | Earns/earning a return | Approved for recovery | Cook Plant Uprate Project
Regulatory Asset [Line Items]
Remaining Recovery Period		8 years
Total Noncurrent Regulatory Assets	21	$ 18
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		9 years
Total Noncurrent Regulatory Assets	10	$ 9
INDIANA MICHIGAN POWER COMPANY | Earns/earning a return | Approved for recovery | Cook Plant Turbine - Indiana
Regulatory Asset [Line Items]
Remaining Recovery Period		13 years
Total Noncurrent Regulatory Assets	8	$ 7
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	21	22
INDIANA MICHIGAN POWER COMPANY | Does not earns/earning a return | Pending final regulatory approval
Regulatory Asset [Line Items]
Total Noncurrent Regulatory Assets	109	114
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	2	7
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	74	78
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	6	29
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	27	0
INDIANA MICHIGAN POWER COMPANY | Does not earns/earning a return | Approved for recovery
Regulatory Asset [Line Items]
Total Noncurrent Regulatory Assets	238	$ 310
INDIANA MICHIGAN POWER COMPANY | Does not earns/earning a return | Approved for recovery | Storm-Related Costs
Regulatory Asset [Line Items]
Remaining Recovery Period		3 years
Total Noncurrent Regulatory Assets	20	$ 14
INDIANA MICHIGAN POWER COMPANY | Does not earns/earning a return | Approved for recovery | NOLC Costs - Indiana
Regulatory Asset [Line Items]
Remaining Recovery Period		2 years
Total Noncurrent Regulatory Assets	0	$ 19
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	28	11
INDIANA MICHIGAN POWER COMPANY | Does not earns/earning a return | Approved for recovery | Income Taxes, Net
Regulatory Asset [Line Items]
Total Noncurrent Regulatory Assets	109	165
Regulatory asset, not subject to rate normalization requirements, amount	$ 12	$ 6
Regulatory asset, not subject to rate normalization requirements, refund period	2 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	$ 43	$ 82
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		23 years
Total Noncurrent Regulatory Assets	11	$ 10
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		3 years
Total Noncurrent Regulatory Assets	12	$ 9
INDIANA MICHIGAN POWER COMPANY | Does not earns/earning a return | Approved for recovery | Pension and OPEB Funded Status
Regulatory Asset [Line Items]
Total Noncurrent Regulatory Assets	$ 15	$ 0