Other Comprehensive Loss - Amounts Reclassified from Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of actuarial (gains) losses and prior service costs	$ (2.1)	$ (1.0)	$ 5.6	$ (3.3)
Total before tax	(261.8)	(228.4)	(620.1)	(585.9)
Provision for income taxes	52.8	49.7	132.8	129.2
Total net of tax	(209.1)	(178.7)	(487.5)	(456.9)
Reclassification out of Accumulated Other Comprehensive Income | Net Prior Service Attributable to Parent
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of actuarial (gains) losses and prior service costs	(0.3)	0.6	(1.0)	2.5
Reclassification out of Accumulated Other Comprehensive Income | Retirement Benefits Adjustment
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	(0.3)	0.6	(1.0)	2.5
Provision for income taxes	0.0	0.0	0.2	(0.7)
Total net of tax	$ (0.3)	$ 0.6	$ (0.8)	$ 1.8