Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018
Supplemental Cash Flow Elements [Abstract]
Interest paid	$ 6.1	$ 0.3
Non-cash investing and financing activities (included in Accounts Payable):
Unpaid purchases of property and equipment	4.7	4.7
Stock repurchases not yet settled	0.0	0.2
Supplemental lease disclosures:
Operating lease liabilities arising from obtaining operating lease assets	4.2	0.5
Cash paid for amounts included in the measurement of operating lease liabilities	1.1	0.9
Right-of-Use Asset Obtained in Exchange for Finance Lease Liability	0.1	0.0
Components of cash, cash equivalents and restricted cash:
Cash and cash equivalents	307.2	115.3	$ 264.3
Restricted cash included in Prepaid expenses and other current assets	0.0	0.3
Restricted cash included in Other assets	13.9	13.8
Total cash, cash equivalents and restricted cash presented on our Statements of Consolidated Cash Flows	$ 321.1	$ 129.4	$ 278.6	$ 139.6