Revenue from Contracts with Customers - Provision for Doubtful Accounts (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Change in the allowance for doubtful accounts
Balance at beginning of year	$ 9.0	$ 7.0	$ 7.5	$ 7.5
Provision charged to expense	3.8	3.8	9.1	7.3
Accounts written off, net of recoveries	(5.0)	(2.6)	(8.8)	(6.6)
Balance at end of year	7.8	$ 8.2	7.8	$ 8.2
Allowance for doubtful accounts for non-trade accounts receivable	$ 3.1		$ 3.1