SIGNIFICANT ACCOUNTING MATTERS - Reconciliation of Cash (Details) - USD ($) $ in Millions	Mar. 31, 2026	Dec. 31, 2025	Mar. 31, 2025	Dec. 31, 2024
Significant Accounting Matters [Line Items]
Cash and Cash Equivalents	$ 306	$ 197
Restricted Cash	33	71
Total Cash, Cash Equivalents and Restricted Cash	339	268	$ 292	$ 246
AEP Texas
Significant Accounting Matters [Line Items]
Cash and Cash Equivalents	0	0
Restricted Cash	6	14
Total Cash, Cash Equivalents and Restricted Cash	6	14	14	24
APCo
Significant Accounting Matters [Line Items]
Cash and Cash Equivalents	4	5
Restricted Cash	12	18
Total Cash, Cash Equivalents and Restricted Cash	16	23	19	20
SWEPCo
Significant Accounting Matters [Line Items]
Cash and Cash Equivalents	2	2
Restricted Cash	7	15
Total Cash, Cash Equivalents and Restricted Cash	$ 9	$ 17	$ 15	$ 5