Regulatory Assets and Liabilities - Regulatory Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Regulatory liabilities
Other current liabilities	$ 45.3	$ 47.5
Regulatory liabilities	3,958.0	3,697.7
Total regulatory liabilities	4,003.3	3,745.2
Income tax related items
Regulatory liabilities
Total regulatory liabilities	1,825.4	1,901.8
Removal costs
Regulatory liabilities
Total regulatory liabilities	1,458.2	1,329.9
Pension and OPEB benefits
Regulatory liabilities
Total regulatory liabilities	308.5	299.2
Energy costs refundable through rate adjustments
Regulatory liabilities
Total regulatory liabilities	160.8	72.4
Uncollectible expense
Regulatory liabilities
Total regulatory liabilities	47.2	21.2
Revenue requirements of renewable generation facilities
Regulatory liabilities
Total regulatory liabilities	44.2	0.0
Derivatives
Regulatory liabilities
Total regulatory liabilities	36.9	19.2
Electric transmission costs
Regulatory liabilities
Total regulatory liabilities	19.7	30.3
Other, net
Regulatory liabilities
Total regulatory liabilities	$ 102.4	$ 71.2