Commitments and Contingent Liabilities - Schedule of Expected Aggregate Undiscounted Amount to Amounts Recognized (Details) - Black lung Benefit - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Loss Contingencies [Line Items]
Black lung liability, undiscounted	$ 27.1	$ 96.0
Impact of discounting	(12.7)	(37.8)
Black lung liability, discounted	$ 14.4	$ 58.2