Balance Sheet Accounts and Supplemental Disclosures - Accumulated Other Comprehensive Loss, Net of Income Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 233.5	$ 576.7
Actuarial losses, net of income taxes	80.5	(31.5)
Amortization of net actuarial losses and prior service credits, net of income taxes	46.1	40.4
Ending balance	533.5	233.5
Actuarial Losses, Net
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(227.6)	(236.4)
Actuarial losses, net of income taxes	80.5	(31.5)
Amortization of net actuarial losses and prior service credits, net of income taxes	46.0	40.3
Ending balance	(101.1)	(227.6)
Prior Service Credits (Costs), Net
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	0.0	(0.1)
Actuarial losses, net of income taxes	0.0	0.0
Amortization of net actuarial losses and prior service credits, net of income taxes	0.1	0.1
Ending balance	0.1	0.0
AOCI Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(227.6)	(236.5)
Ending balance	$ (101.0)	$ (227.6)