Fair Value Measurements: Other Fair Value Measurements (Details) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Carrying Amount
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt, including current maturities	$ 4,847.1	$ 4,401.2
Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt, including current maturities	$ 4,589.6	$ 4,215.6