Revenue from Contracts with Customers - Provision for Doubtful Accounts (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Trade accounts receivable
Threshold period past due for trade accounts receivable for disconnecting service to customers	60 days
Change in the allowance for doubtful accounts
Balance at beginning of period	$ 8.6
Provision charged to expense	2.9	$ 7.3
Balance at end of period	9.1
Trade accounts receivable
Change in the allowance for doubtful accounts
Balance at beginning of period	8.6	7.5
Provision charged to expense	2.9	5.3
Accounts written off, net of recoveries	(2.4)	(3.8)
Balance at end of period	9.1	9.0
Non-trade accounts receivable
Change in the allowance for doubtful accounts
Balance at end of period	$ 0.0	$ 2.0