Property and Equipment - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Abstract]
Property, software and equipment depreciation, amortization expense	$ 341.4	$ 307.7	$ 272.5
Capitalization of stock-based compensation	28.9	23.1	$ 17.9
Disposal of property plant and equipment	174.6	$ 93.4
Write off of internal-use software	36.2
Net book value of internal-use software	$ 32.0