Accounting Policies - Disaggregation of Revenue (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenue from External Customer [Line Items]
Total revenue	$ 4,513.7	$ 4,871.2	$ 5,092.0
LTL revenue
Revenue from External Customer [Line Items]
Total revenue	4,093.3	4,494.0	4,690.6
Other revenue
Revenue from External Customer [Line Items]
Total revenue	$ 420.4	$ 377.2	$ 401.4