Income Taxes - Net deferred tax assets (liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Lease liability	$ 119.6	$ 125.9
Employee compensation	7.5	9.2
Revenue recognition	36.6	32.8
Other	10.2	5.9
Deferred tax assets	173.9	173.8
Valuation allowance	(3.0)	(1.5)
Total deferred tax assets after valuation allowance	170.9	172.3
Recognition of franchise and equipment sales	(10.7)	(13.7)
Capitalization and depreciation	(123.2)	(130.8)
Lease assets (1)	(114.2)	(125.8)
Other	(1.1)	(0.5)
Deferred tax liabilities	(249.2)	(270.8)
Net deferred tax liabilities	$ (78.3)	$ (98.5)