Revenue from Contracts with Customers - Costs of Obtaining Contracts (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018
Costs of Obtaining Contracts with Customers
Capitalized contract cost, Beginning of period	$ 26.3
Impact of change in accounting policy		$ 11.4
Deferral	22.2	19.0
Amortization	(7.8)	(4.1)
Capitalized contract cost, End of period	40.7	26.3
Current costs of obtaining contracts with customers			$ 10.0	$ 6.0
Non-current costs of obtaining contracts with customers			30.7	20.3
Total costs of obtaining contracts with customers	$ 26.3	$ 26.3	$ 40.7	$ 26.3
Residential Subscription | Minimum
Costs of Obtaining Contracts with Customers
Costs of contracts with customers, amortization period			3 years
Residential Subscription | Maximum
Costs of Obtaining Contracts with Customers
Costs of contracts with customers, amortization period			4 years
Business Subscription | Minimum
Costs of Obtaining Contracts with Customers
Costs of contracts with customers, amortization period			6 years
Business Subscription | Maximum
Costs of Obtaining Contracts with Customers
Costs of contracts with customers, amortization period			7 years