RATE MATTERS - Regulatory Assets Subject to Securitization (Details) - APCo $ in Millions	Sep. 30, 2025 USD ($)
Regulatory Asset [Line Items]
Regulatory asset, requested to be financed through securitization	$ 2,527.6
Undepreciated Utility Plant Balances of Amos, Mitchell and Mountaineer (as of December 31, 2022)
Regulatory Asset [Line Items]
Regulatory asset, requested to be financed through securitization	1,704.2
ENEC Under-Recovery Regulatory Assets
Regulatory Asset [Line Items]
Regulatory asset, requested to be financed through securitization	412.4
Forecasted Undepreciated CCR and ELG Investments of Amos, Mitchell and Mountaineer (as of November 30, 2024)
Regulatory Asset [Line Items]
Regulatory asset, requested to be financed through securitization	236.8
Deferred Storm O&M Expense Regulatory Assets
Regulatory Asset [Line Items]
Regulatory asset, requested to be financed through securitization	157.9
Upfront Financing Costs
Regulatory Asset [Line Items]
Regulatory asset, requested to be financed through securitization	16.3
APCo Portion
Regulatory Asset [Line Items]
Regulatory asset, requested to be financed through securitization	1,565.1
APCo Portion | Undepreciated Utility Plant Balances of Amos, Mitchell and Mountaineer (as of December 31, 2022)
Regulatory Asset [Line Items]
Regulatory asset, requested to be financed through securitization	1,145.5
APCo Portion | ENEC Under-Recovery Regulatory Assets
Regulatory Asset [Line Items]
Regulatory asset, requested to be financed through securitization	166.6
APCo Portion | Forecasted Undepreciated CCR and ELG Investments of Amos, Mitchell and Mountaineer (as of November 30, 2024)
Regulatory Asset [Line Items]
Regulatory asset, requested to be financed through securitization	87.6
APCo Portion | Deferred Storm O&M Expense Regulatory Assets
Regulatory Asset [Line Items]
Regulatory asset, requested to be financed through securitization	155.0
APCo Portion | Upfront Financing Costs
Regulatory Asset [Line Items]
Regulatory asset, requested to be financed through securitization	10.4
WPCo Portion
Regulatory Asset [Line Items]
Regulatory asset, requested to be financed through securitization	962.5
WPCo Portion | Undepreciated Utility Plant Balances of Amos, Mitchell and Mountaineer (as of December 31, 2022)
Regulatory Asset [Line Items]
Regulatory asset, requested to be financed through securitization	558.7
WPCo Portion | ENEC Under-Recovery Regulatory Assets
Regulatory Asset [Line Items]
Regulatory asset, requested to be financed through securitization	245.8
WPCo Portion | Forecasted Undepreciated CCR and ELG Investments of Amos, Mitchell and Mountaineer (as of November 30, 2024)
Regulatory Asset [Line Items]
Regulatory asset, requested to be financed through securitization	149.2
WPCo Portion | Deferred Storm O&M Expense Regulatory Assets
Regulatory Asset [Line Items]
Regulatory asset, requested to be financed through securitization	2.9
WPCo Portion | Upfront Financing Costs
Regulatory Asset [Line Items]
Regulatory asset, requested to be financed through securitization	$ 5.9