Revenue from Contracts with Customers - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Jun. 30, 2018	Dec. 31, 2017	Jan. 01, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Percentage of consolidated revenue		61.00%
Management fee, percentage		8.00%
Service fee retained by Sprint		8.60%
Management fee on prepaid wireless revenues and costs		6.00%
Average subscriber life		2 years
Wireless contract asset balance	$ 44.1	$ 44.1		$ 42.8
Payments to increase wireless contract asset balance	14.6	28.4
Amortization to reduce revenue	13.7	$ 27.1
Revenue recorded from equipment financing transactions			$ 63.8
Estimated customer life (in months)		42 months
Cost to fulfill contract	9.8	$ 9.8
Amortization of capitalized costs to fulfill contracts	2.7	$ 2.7
Cable
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Installation revenue, recognition period		10 months
Commissions and other costs, recognition period (in months)		44 months
Wireline
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Installation revenue, recognition period		11 months
Commissions and other costs, recognition period (in months)		72 months
Enterprise
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Commissions and other costs, recognition period (in months)		46 months
Prepaid expenses and other
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cost to fulfill contract	4.6	$ 4.6
Deferred charges and other assets, net
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cost to fulfill contract	$ 5.2	$ 5.2
Cost of Goods and Services Sold
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reimbursement payments, cost of equipment and commissions			63.5
Selling, General and Administrative Expenses
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reimbursement payments, cost of equipment and commissions			$ 16.9