SIGNIFICANT ACCOUNTING MATTERS - Reconciliation of Cash (Details) - USD ($) $ in Millions |
Sep. 30, 2026 |
Dec. 31, 2025 |
Sep. 30, 2025 |
Dec. 31, 2024 |
|---|---|---|---|---|
| Significant Accounting Matters [Line Items] | ||||
| Cash and Cash Equivalents | $ 418 | $ 197 | ||
| Restricted Cash | 89 | 71 | ||
| Total Cash, Cash Equivalents and Restricted Cash | 507 | 268 | $ 1,107 | $ 246 |
| AEP Texas | ||||
| Significant Accounting Matters [Line Items] | ||||
| Cash and Cash Equivalents | 0 | 0 | ||
| Restricted Cash | 9 | 14 | ||
| Total Cash, Cash Equivalents and Restricted Cash | 9 | 14 | 7 | 24 |
| APCo | ||||
| Significant Accounting Matters [Line Items] | ||||
| Cash and Cash Equivalents | 4 | 5 | ||
| Restricted Cash | 60 | 18 | ||
| Total Cash, Cash Equivalents and Restricted Cash | 64 | 23 | 15 | 20 |
| SWEPCo | ||||
| Significant Accounting Matters [Line Items] | ||||
| Cash and Cash Equivalents | 3 | 2 | ||
| Restricted Cash | 6 | 15 | ||
| Total Cash, Cash Equivalents and Restricted Cash | $ 9 | $ 17 | $ 11 | $ 5 |