Summary of Significant Accounting Policies - Assets Held for Sale (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Long Lived Assets Held-for-sale [Line Items]
Impairment on assets held for sale	$ 14.3	$ 0.3	$ 1.4
Assets held for sale, net of impairment	67.4	21.9
Truckload
Long Lived Assets Held-for-sale [Line Items]
Assets held for sale, net of impairment	63.5	19.5
Intermodal
Long Lived Assets Held-for-sale [Line Items]
Assets held for sale, net of impairment	3.9	$ 2.4
FTFM service offering shutdown
Long Lived Assets Held-for-sale [Line Items]
Impairment on assets held for sale	28.1
Assets held for sale, net of impairment	33.4
Bulk sale of tractors
Long Lived Assets Held-for-sale [Line Items]
Impairment on assets held for sale	11.5
Non FTFM Shutdown and FTFM Shutdown
Long Lived Assets Held-for-sale [Line Items]
Impairment on assets held for sale	$ 42.4