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BENEFIT PLANS - Components of Net Periodic Benefit Cost (Credit) (Details) - USD ($) $ in Millions | 3 Months Ended
--- | ---
Mar. 31, 2025 | Mar. 31, 2024
Pension Plans |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Service Cost | $ 24.0 | $ 25.6
Interest Cost | 52.8 | 51.9
Expected Return on Plan Assets | (70.3) | (80.2)
Amortization of Net Actuarial Loss | 4.1 | 1.1
Net Periodic Benefit Cost (Credit) | 10.6 | (1.6)
Pension Plans | AEP Texas |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Service Cost | 2.2 | 2.2
Interest Cost | 4.5 | 4.3
Expected Return on Plan Assets | (5.6) | (6.4)
Amortization of Net Actuarial Loss | 0.3 | 0.1
Net Periodic Benefit Cost (Credit) | 1.4 | 0.2
Pension Plans | APCo |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Service Cost | 2.4 | 2.4
Interest Cost | 6.2 | 6.2
Expected Return on Plan Assets | (9.4) | (10.7)
Amortization of Net Actuarial Loss | 0.4 | 0.1
Net Periodic Benefit Cost (Credit) | (0.4) | (2.0)
Pension Plans | I&M |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Service Cost | 3.2 | 3.3
Interest Cost | 6.2 | 6.0
Expected Return on Plan Assets | (9.7) | (10.8)
Amortization of Net Actuarial Loss | 0.4 | 0.1
Net Periodic Benefit Cost (Credit) | 0.1 | (1.4)
Pension Plans | OPCo |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Service Cost | 2.3 | 2.4
Interest Cost | 4.9 | 4.7
Expected Return on Plan Assets | (7.3) | (8.2)
Amortization of Net Actuarial Loss | 0.3 | 0.1
Net Periodic Benefit Cost (Credit) | 0.2 | (1.0)
Pension Plans | PSO |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Service Cost | 1.4 | 1.5
Interest Cost | 2.7 | 2.5
Expected Return on Plan Assets | (3.9) | (4.3)
Amortization of Net Actuarial Loss | 0.2 | 0.0
Net Periodic Benefit Cost (Credit) | 0.4 | (0.3)
Pension Plans | SWEPCo |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Service Cost | 1.9 | 1.9
Interest Cost | 3.2 | 3.1
Expected Return on Plan Assets | (3.7) | (4.4)
Amortization of Net Actuarial Loss | 0.2 | 0.1
Net Periodic Benefit Cost (Credit) | 1.6 | 0.7
OPEB |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Service Cost | 0.8 | 1.1
Interest Cost | 8.6 | 10.5
Expected Return on Plan Assets | (28.2) | (27.8)
Amortization of Prior Service Credit | (0.6) | (3.2)
Amortization of Net Actuarial Loss | (0.3) | 0.8
Net Periodic Benefit Cost (Credit) | (19.7) | (18.6)
OPEB | AEP Texas |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Service Cost | 0.1 | 0.1
Interest Cost | 0.6 | 0.8
Expected Return on Plan Assets | (2.3) | (2.3)
Amortization of Prior Service Credit | 0.0 | (0.3)
Amortization of Net Actuarial Loss | 0.0 | 0.1
Net Periodic Benefit Cost (Credit) | (1.6) | (1.6)
OPEB | APCo |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Service Cost | 0.1 | 0.1
Interest Cost | 1.4 | 1.7
Expected Return on Plan Assets | (4.1) | (4.0)
Amortization of Prior Service Credit | (0.1) | (0.5)
Amortization of Net Actuarial Loss | (0.1) | 0.1
Net Periodic Benefit Cost (Credit) | (2.8) | (2.6)
OPEB | I&M |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Service Cost | 0.1 | 0.1
Interest Cost | 1.0 | 1.2
Expected Return on Plan Assets | (3.4) | (3.4)
Amortization of Prior Service Credit | (0.1) | (0.4)
Amortization of Net Actuarial Loss | 0.0 | 0.1
Net Periodic Benefit Cost (Credit) | (2.4) | (2.4)
OPEB | OPCo |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Service Cost | 0.1 | 0.1
Interest Cost | 0.8 | 1.1
Expected Return on Plan Assets | (2.9) | (3.0)
Amortization of Prior Service Credit | (0.1) | (0.3)
Amortization of Net Actuarial Loss | 0.0 | 0.1
Net Periodic Benefit Cost (Credit) | (2.1) | (2.0)
OPEB | PSO |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Service Cost | 0.0 | 0.1
Interest Cost | 0.4 | 0.5
Expected Return on Plan Assets | (1.5) | (1.4)
Amortization of Prior Service Credit | 0.0 | (0.2)
Amortization of Net Actuarial Loss | 0.0 | 0.0
Net Periodic Benefit Cost (Credit) | (1.1) | (1.0)
OPEB | SWEPCo |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Service Cost | 0.1 | 0.1
Interest Cost | 0.5 | 0.7
Expected Return on Plan Assets | (1.9) | (1.9)
Amortization of Prior Service Credit | 0.0 | (0.3)
Amortization of Net Actuarial Loss | 0.0 | 0.1
Net Periodic Benefit Cost (Credit) | $ (1.3) | $ (1.3)

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- Definition Amount of prior service cost (credit) recognized in net periodic benefit cost (credit) of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 17 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480482/715-20-55-17 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 45 -Paragraph 3A -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480535/715-20-45-3A Reference 3: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 18 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480482/715-20-55-18 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (h)(5) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 6 -Subparagraph (a)(5) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-6 + Details
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- Definition Amount of expected return (loss) recognized in net periodic benefit (cost) credit, calculated based on expected long-term rate of return and market-related value of plan assets of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 17 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480482/715-20-55-17 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 45 -Paragraph 3A -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480535/715-20-45-3A Reference 3: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 18 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480482/715-20-55-18 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (h)(3) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 6 -Subparagraph (a)(3) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-6 + Details
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