Lease Obligations (Operating Leases) (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Lease Terms in Excess of One Year [Member]
Operating Leases [Line Items]
Operating leases, rent and related expense (in dollars)	$ 104.2	$ 100.5	$ 81.8
Lease Terms in Excess of One Year [Member] | Minimum [Member]
Operating Leases [Line Items]
Operating leases, term of contract (in years)	1 year	1 year	1 year
Lease Terms of One Year or Less [Member]
Operating Leases [Line Items]
Operating leases, rent and related expense (in dollars)	$ 461.0	$ 298.0	$ 196.2
Lease Terms of One Year or Less [Member] | Maximum [Member]
Operating Leases [Line Items]
Operating leases, term of contract (in years)	1 year	1 year	1 year