PROPERTY, PLANT, AND EQUIPMENT - Proportionate Share of Operating Costs (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Property, Plant and Equipment [Line Items]
Utility Plant in Service	$ 1,921.1	$ 1,906.8
Construction Work in Progress	4.6	11.7
Accumulated Depreciation	539.0	490.8
SOUTHWESTERN ELECTRIC POWER COMPANY
Property, Plant and Equipment [Line Items]
Utility Plant in Service	3,014.6	2,993.1
Construction Work in Progress	5.8	14.6
Accumulated Depreciation	$ 637.1	$ 558.7
Flint Creek Generating Station (Unit No. 1) | Coal
Property, Plant and Equipment [Line Items]
Percent of Ownership	50.00%	50.00%
Utility Plant in Service	$ 404.1	$ 402.8
Construction Work in Progress	3.4	1.6
Accumulated Depreciation	$ 188.8	$ 167.5
Flint Creek Generating Station (Unit No. 1) | Coal | SOUTHWESTERN ELECTRIC POWER COMPANY
Property, Plant and Equipment [Line Items]
Percent of Ownership	50.00%	50.00%
Utility Plant in Service	$ 404.1	$ 402.8
Construction Work in Progress	3.4	1.6
Accumulated Depreciation	$ 188.8	$ 167.5
Turk Generating Plant | Coal
Property, Plant and Equipment [Line Items]
Percent of Ownership	73.30%	73.30%
Utility Plant in Service	$ 1,517.0	$ 1,504.0
Construction Work in Progress	1.2	10.1
Accumulated Depreciation	$ 350.2	$ 323.3
Turk Generating Plant | Coal | SOUTHWESTERN ELECTRIC POWER COMPANY
Property, Plant and Equipment [Line Items]
Percent of Ownership	73.30%	73.30%
Utility Plant in Service	$ 1,517.0	$ 1,504.0
Construction Work in Progress	1.2	10.1
Accumulated Depreciation	$ 350.2	$ 323.3
Rockport Generating Plant | AEGCo
Property, Plant and Equipment [Line Items]
Percent of Ownership	50.00%
Rockport Generating Plant | Coal | INDIANA MICHIGAN POWER COMPANY
Property, Plant and Equipment [Line Items]
Percent of Ownership	50.00%	50.00%
Utility Plant in Service	$ 1,345.0	$ 1,341.4
Construction Work in Progress	10.9	7.9
Accumulated Depreciation	$ 1,181.8	$ 1,018.9
North Central Wind Energy Facilities | PUBLIC SERVICE COMPANY OF OKLAHOMA
Property, Plant and Equipment [Line Items]
Percent of Ownership	45.50%
North Central Wind Energy Facilities | SOUTHWESTERN ELECTRIC POWER COMPANY
Property, Plant and Equipment [Line Items]
Percent of Ownership	54.50%
North Central Wind Energy Facilities | Wind | PUBLIC SERVICE COMPANY OF OKLAHOMA
Property, Plant and Equipment [Line Items]
Percent of Ownership	45.50%	45.50%
Utility Plant in Service	$ 912.3	$ 906.3
Construction Work in Progress	1.0	2.4
Accumulated Depreciation	$ 77.6	$ 54.1
North Central Wind Energy Facilities | Wind | SOUTHWESTERN ELECTRIC POWER COMPANY
Property, Plant and Equipment [Line Items]
Percent of Ownership	54.50%	54.50%
Utility Plant in Service	$ 1,093.5	$ 1,086.3
Construction Work in Progress	1.2	2.9
Accumulated Depreciation	$ 98.1	$ 67.9