REVENUE FROM CONTRACTS WITH CUSTOMERS - Performance Obligation (Details) $ in Millions	Mar. 31, 2026 USD ($)
Disaggregation of Revenue [Line Items]
Fixed performance obligations	$ 205
APPALACHIAN POWER COMPANY
Disaggregation of Revenue [Line Items]
Fixed performance obligations	80
INDIANA MICHIGAN POWER COMPANY
Disaggregation of Revenue [Line Items]
Fixed performance obligations	19
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-04-01
Disaggregation of Revenue [Line Items]
Fixed performance obligations	$ 64
Revenue, remaining performance obligation, expected timing of satisfaction, period	9 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-04-01 | APPALACHIAN POWER COMPANY
Disaggregation of Revenue [Line Items]
Fixed performance obligations	$ 12
Revenue, remaining performance obligation, expected timing of satisfaction, period	9 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-04-01 | INDIANA MICHIGAN POWER COMPANY
Disaggregation of Revenue [Line Items]
Fixed performance obligations	$ 3
Revenue, remaining performance obligation, expected timing of satisfaction, period	9 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2027-01-01
Disaggregation of Revenue [Line Items]
Fixed performance obligations	$ 86
Revenue, remaining performance obligation, expected timing of satisfaction, period	2 years
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2027-01-01 | APPALACHIAN POWER COMPANY
Disaggregation of Revenue [Line Items]
Fixed performance obligations	$ 32
Revenue, remaining performance obligation, expected timing of satisfaction, period	2 years
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2027-01-01 | INDIANA MICHIGAN POWER COMPANY
Disaggregation of Revenue [Line Items]
Fixed performance obligations	$ 9
Revenue, remaining performance obligation, expected timing of satisfaction, period	2 years
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2029-01-01
Disaggregation of Revenue [Line Items]
Fixed performance obligations	$ 39
Revenue, remaining performance obligation, expected timing of satisfaction, period	2 years
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2029-01-01 | APPALACHIAN POWER COMPANY
Disaggregation of Revenue [Line Items]
Fixed performance obligations	$ 24
Revenue, remaining performance obligation, expected timing of satisfaction, period	2 years
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2029-01-01 | INDIANA MICHIGAN POWER COMPANY
Disaggregation of Revenue [Line Items]
Fixed performance obligations	$ 5
Revenue, remaining performance obligation, expected timing of satisfaction, period	2 years
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2031-01-01
Disaggregation of Revenue [Line Items]
Fixed performance obligations	$ 16
Revenue, remaining performance obligation, expected timing of satisfaction, period
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2031-01-01 | APPALACHIAN POWER COMPANY
Disaggregation of Revenue [Line Items]
Fixed performance obligations	$ 12
Revenue, remaining performance obligation, expected timing of satisfaction, period
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2031-01-01 | INDIANA MICHIGAN POWER COMPANY
Disaggregation of Revenue [Line Items]
Fixed performance obligations	$ 2
Revenue, remaining performance obligation, expected timing of satisfaction, period