Revenue Recognition and Related Costs (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Jan. 01, 2018
Revenue from Contract with Customer [Abstract]
Trade receivables, allowance for doubtful accounts	$ 55.6	$ 55.6	$ 89.5
Contract assets	38.0	38.0	26.1
Deferred revenue	802.3	802.3	1,005.2
Revenue recognized		781.3
Aggregate assets associated with incremental costs to obtain a contract and contract fulfillment costs	69.9	69.9	$ 68.1
Amortization related to contract costs	$ 21.5	$ 72.8
Unsatisfied performance obligations, description of timing		Revenue from customers who are subject to contracts is generally recognized over the term of such contracts, which is typically 12 months for our residential service, one to three years for our mobile contracts and one to five years for our B2B contracts.