Operating Revenues - Contract Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Amortization of deferred contract costs	$ 20.7	$ 13.9
Prepaid Expenses and Other Current Assets
Disaggregation of Revenue [Line Items]
Long term deferred costs	13.2	9.8
Other assets
Disaggregation of Revenue [Line Items]
Long term deferred costs	$ 24.2	$ 23.1