Revenue from Contracts with Customers - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Management fee, percentage	8.00%
Service fee retained by Sprint	8.60%
Management fee on prepaid wireless revenues and costs	6.00%
Wireless contract asset balance	$ 65.7		$ 51.1
Payments to increase wireless contract asset balance	61.2
Amortization to reduce revenue	$ 46.6
Revenue recorded from equipment financing transactions		$ 63.8
Estimated customer life (in months)	42 months
Cost to fulfill contract	$ 10.1
Amortization of capitalized costs to fulfill contracts	$ 5.5
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
Deferred charges and other assets, net
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cost to fulfill contract	$ 5.5
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
Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reimbursement payment, cost of equipment and commissions, benefit period for recognition	21 months
Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reimbursement payment, cost of equipment and commissions, benefit period for recognition	53 months