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Short-Term and Long-Term Debt (Tables) | 12 Months Ended
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Dec. 31, 2023
Debt Disclosure [Abstract] |
Long-term Debt |
Long-Term Debt |  |
As of December 31 | 2023 | 2022
Millions |  |
First Mortgage Bonds |  |
6.02% Series Due 2023 | — | $75.0
3.69% Series Due 2024 | $60.0 | 60.0
4.90% Series Due 2025 | 30.0 | 30.0
5.10% Series Due 2025 | 30.0 | 30.0
3.20% Series Due 2026 | 75.0 | 75.0
5.99% Series Due 2027 | 60.0 | 60.0
3.30% Series Due 2028 | 40.0 | 40.0
4.08% Series Due 2029 | 70.0 | 70.0
3.74% Series Due 2029 | 50.0 | 50.0
2.50% Series Due 2030 | 46.0 | 46.0
3.86% Series Due 2030 | 60.0 | 60.0
2.79% Series Due 2031 | 100.0 | 100.0
4.54% Series Due 2032 | 75.0 | 75.0
4.98% Series Due 2033 | 125.0 | —
5.69% Series Due 2036 | 50.0 | 50.0
6.00% Series Due 2040 | 35.0 | 35.0
5.82% Series Due 2040 | 45.0 | 45.0
4.08% Series Due 2042 | 85.0 | 85.0
4.21% Series Due 2043 | 60.0 | 60.0
4.95% Series Due 2044 | 40.0 | 40.0
5.05% Series Due 2044 | 40.0 | 40.0
4.39% Series Due 2044 | 50.0 | 50.0
4.07% Series Due 2048 | 60.0 | 60.0
4.47% Series Due 2049 | 30.0 | 30.0
3.30% Series Due 2050 | 94.0 | 94.0
Armenia Mountain Senior Secured Notes 3.26% Due 2024 | 9.5 | 19.3
Industrial Development Variable Rate Demand Refunding Revenue Bonds Series 2006, Due 2025 | 27.8 | 27.8
Revolving Credit Facility Variable Rate Due 2027 | — | 13.0
Senior Unsecured Notes 2.65% Due 2025 | 150.0 | 150.0
Senior Unsecured Notes 3.11% Due 2027 | 80.0 | 80.0
SWL&P First Mortgage Bonds 4.15% Series Due 2028 | 15.0 | 15.0
SWL&P First Mortgage Bonds 4.14% Series Due 2048 | 12.0 | 12.0
Unsecured Term Loan Variable Rate Due 2023 | — | 170.0
Other Long-Term Debt, 2023 Weighted Average Rate 5.24% Due 2024 – 2051 | 95.1 | 82.0
Unamortized Debt Issuance Costs | (8.1) | (8.3)
Total Long-Term Debt | 1,791.3 | 1,920.8
Less: Due Within One Year | 111.4 | 272.6
Net Long-Term Debt | $1,679.9 | $1,648.2

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