Revenue Recognition and Related Costs (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Revenue from Contract with Customer [Abstract]
Trade receivables, allowance for doubtful accounts	$ 42.9		$ 42.9		$ 45.8
Contract assets	42.6		42.6		44.3
Deferred revenue	822.6		822.6		877.9
Revenue recognized			791.7
Aggregate assets associated with incremental costs to obtain a contract and contract fulfillment costs	72.7		72.7		$ 73.0
Amortization related to contract costs	$ 24.3	$ 28.5	$ 48.7	$ 51.3