Other Comprehensive (Loss) Income - Amounts Reclassified from Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of net (gain) loss	$ (2.3)	$ (0.8)
Reclassification adjustments	9.5	10.7
Total before tax	180.4	145.6
Provision for income taxes	40.5	32.9
Net income	(140.0)	(112.7)
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 net (gain) loss	0.8	1.1
Reclassification out of Accumulated Other Comprehensive Income | Retirement Benefits Adjustment
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	0.8	1.1
Provision for income taxes	(0.2)	(0.3)
Net income	0.6	0.8
Reclassification out of Accumulated Other Comprehensive Income | Cumulative Unrealized Gain (Loss) on Derivatives
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification adjustments	0.0	0.9
Total before tax	0.0	0.9
Provision for income taxes	0.0	(0.2)
Net income	$ 0.0	$ 0.7