Fair Value Measurements - Financial Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Financial instruments
Preferred stock of subsidiary	$ 30.4	$ 30.4
Long-term debt, including current portion	18,907.1	16,631.1
Carrying amount
Financial instruments
Preferred stock of subsidiary	30.4	30.4
Long-term debt, including current portion	18,907.1	16,631.1
Fair value
Financial instruments
Preferred stock of subsidiary	21.2	21.4
Long-term debt, including current portion	$ 17,840.8	$ 15,564.3