Retirement Benefits - Retirement Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Total
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 8.7	$ 7.6	$ 8.1
Interest cost on projected benefit obligation	48.4	50.5	36.0
Return on assets – expected	(57.8)	(58.3)	(61.4)
Amortization of losses	7.8	3.4	26.2
Amortization of prior service cost	0.1	0.0	0.0
Curtailment gain	0.0	0.0	(0.5)
Settlement loss	1.1	0.0	3.2
Net periodic pension cost (credit)	8.3	3.2	11.6
Retirement benefits other than pension
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.1	0.3	0.1
Interest cost on projected benefit obligation	14.2	16.4	14.0
Return on assets – expected	(10.2)	(10.3)	(13.2)
Amortization of losses	6.0	9.9	17.3
Amortization of prior service cost	(9.4)	(11.1)	(4.9)
Net periodic pension cost (credit)	0.7	5.2	13.3
UMWA Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.0	0.0	0.0
Interest cost on projected benefit obligation	9.6	11.1	10.3
Return on assets – expected	(10.2)	(10.3)	(13.2)
Amortization of losses	1.7	5.1	10.0
Amortization of prior service cost	(9.4)	(11.0)	(4.6)
Net periodic pension cost (credit)	(8.3)	(5.1)	2.5
Black Lung and Other Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.1	0.3	0.1
Interest cost on projected benefit obligation	4.6	5.3	3.7
Return on assets – expected	0.0	0.0	0.0
Amortization of losses	4.3	4.8	7.3
Amortization of prior service cost	0.0	(0.1)	(0.3)
Net periodic pension cost (credit)	9.0	10.3	10.8
U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.0	0.0	0.0
Interest cost on projected benefit obligation	30.7	32.4	22.9
Return on assets – expected	(46.4)	(47.2)	(48.7)
Amortization of losses	5.2	1.6	24.2
Amortization of prior service cost	0.0	0.0	0.0
Curtailment gain	0.0	0.0	0.0
Settlement loss	0.0	0.0	0.0
Net periodic pension cost (credit)	(10.5)	(13.2)	(1.6)
Non-U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	8.7	7.6	8.1
Interest cost on projected benefit obligation	17.7	18.1	13.1
Return on assets – expected	(11.4)	(11.1)	(12.7)
Amortization of losses	2.6	1.8	2.0
Amortization of prior service cost	0.1	0.0	0.0
Curtailment gain	0.0	0.0	(0.5)
Settlement loss	1.1	0.0	3.2
Net periodic pension cost (credit)	$ 18.8	$ 16.4	$ 13.2