Stockholders' Equity - Reclassifications Out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Interest expense, net		$ (152.4)	$ (93.5)	$ (128.8)
Income before taxes		1,108.7	632.7	917.0
Income tax benefit		(267.6)	(171.7)	(220.6)
Net income		841.1	461.0	$ 696.4
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]	(3.4)	(3.9)
Amortization of actuarial gains / (losses)	[1]	(9.9)	(10.4)
Income before taxes		(13.3)	(14.3)
Income tax benefit		3.3	3.6
Net income		$ (10.0)	$ (10.7)

[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.