Retirement Benefits - Retirement Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Total
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 8.1	$ 9.1	$ 9.7
Interest cost on projected benefit obligation	36.0	33.2	38.3
Return on assets – expected	(61.4)	(59.8)	(58.3)
Amortization of losses	26.2	40.6	33.7
Curtailment gain	(0.5)	(0.8)	(1.5)
Settlement loss	3.2	3.3	2.4
Net periodic pension cost (credit)	11.6	25.6	24.3
Retirement benefits other than pension
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.1	0.1	0.1
Interest cost on projected benefit obligation	14.0	13.0	16.5
Return on assets – expected	(13.2)	(12.3)	(13.0)
Amortization of losses	17.3	26.5	24.8
Amortization of prior service cost	(4.9)	(5.0)	(5.0)
Net periodic pension cost (credit)	13.3	22.3	23.4
UMWA Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.0	0.0	0.0
Interest cost on projected benefit obligation	10.3	9.8	12.7
Return on assets – expected	(13.2)	(12.3)	(13.0)
Amortization of losses	10.0	17.5	16.5
Amortization of prior service cost	(4.6)	(4.7)	(4.7)
Net periodic pension cost (credit)	2.5	10.3	11.5
Black Lung and Other Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.1	0.1	0.1
Interest cost on projected benefit obligation	3.7	3.2	3.8
Return on assets – expected	0.0	0.0	0.0
Amortization of losses	7.3	9.0	8.3
Amortization of prior service cost	(0.3)	(0.3)	(0.3)
Net periodic pension cost (credit)	10.8	12.0	11.9
U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.0	0.0	0.0
Interest cost on projected benefit obligation	22.9	21.1	26.7
Return on assets – expected	(48.7)	(47.4)	(46.2)
Amortization of losses	24.2	34.0	28.6
Settlement loss	0.0	0.0	0.0
Net periodic pension cost (credit)	(1.6)	7.7	9.1
Non-U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	8.1	9.1	9.7
Interest cost on projected benefit obligation	13.1	12.1	11.6
Return on assets – expected	(12.7)	(12.4)	(12.1)
Amortization of losses	2.0	6.6	5.1
Curtailment gain	(0.5)	(0.8)	(1.5)
Settlement loss	3.2	3.3	2.4
Net periodic pension cost (credit)	$ 13.2	$ 17.9	$ 15.2