Summary of Significant Accounting Policies - Bad Debt (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Bad Debt
Period of delinquency after which Company disconnects services to customers	60 days
Change in the allowance for doubtful accounts
Balance at beginning of year	$ 7.5	$ 5.8
Provision charged to expense	16.9	20.2	$ 19.7
Accounts written off	(16.9)	(19.7)
Other		1.2
Balance at end of year	$ 7.5	$ 7.5	$ 5.8