Lease Obligations (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Lessee, Lease, Description [Line Items]
Finance leases, assets, gross	$ 628.8		$ 628.8		$ 563.0
Finance Lease, Liability, Statement of Financial Position [Extensible List]	Property and equipment, net		Property and equipment, net		Property and equipment, net
Finance leases, assets, net	$ 466.3		$ 466.3		$ 418.7
Finance leases, assets, depreciation	18.7	$ 16.8	37.7	$ 32.6
Operating leases, additions	79.7	7.5	85.3	13.3
Operating leases, expense	28.1	26.8	55.5	62.1
Operating leases, variable lease costs	2.9	2.8	5.1	5.7
Operating leases, short-term leases, expense	$ 130.8	$ 72.9	$ 240.9	$ 150.4
Finance leases, weighted average remaining lease term (in years)	2 years 6 months		2 years 6 months
Finance leases, weighted average discount rate, percent	3.50%		3.50%
Operating leases, weighted average remaining lease term (in years)	3 years 10 months 24 days		3 years 10 months 24 days
Operating leases, weighted average discount rate, percent	3.10%		3.10%
2021 Acquisitions
Lessee, Lease, Description [Line Items]
Operating leases, additions			$ 74.6
Minimum
Lessee, Lease, Description [Line Items]
Operating leases, term of contract (in years)	1 year		1 year
Minimum | Equipment Leases
Lessee, Lease, Description [Line Items]
Leases, renewal term			1 year
Minimum | Facility Leases
Lessee, Lease, Description [Line Items]
Leases, renewal term			1 year
Maximum
Lessee, Lease, Description [Line Items]
Leases, remaining lease terms			9 years
Operating leases, term of contract (in years)	1 year		1 year
Maximum | Equipment Leases
Lessee, Lease, Description [Line Items]
Leases, renewal term			5 years
Maximum | Facility Leases
Lessee, Lease, Description [Line Items]
Leases, renewal term			5 years