Stockholders' Equity - Reclassifications Out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2025	Mar. 31, 2024
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Income before taxes		$ 267.4	$ 187.5
Income tax expense		(63.6)	(40.6)
Net income		203.8	146.9
Unfunded Employee Benefit Obligations | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Amortization of prior service costs	[1]	(1.4)	(1.3)
Amortization of actuarial losses	[1]	0.1	(0.1)
Income before taxes		(1.3)	(1.4)
Income tax expense		0.3	0.4
Net income		$ (1.0)	$ (1.0)

[1] These AOCI components are included in the computation of net pension and postretirement benefit costs. See Note 13, Employee Benefit Plans and Other Postretirement Benefits, for additional information.