Short-Term and Long-Term Debt (Tables)

12 Months Ended

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