Leases - Components of Lease Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Operating lease income:
Variable lease income	$ 258.6	$ 253.4	$ 764.7	$ 759.1
Operating Lease, Variable Lease Income	13.2	14.9	43.7	50.0
Operating Lease, Lease Income	271.8	268.3	808.4	809.1
Finance lease income	1.5	2.2	4.9	7.7
Total lease income	273.3	270.5	813.3	816.8
Total operating lease income	$ 22.7	$ 22.3	$ 69.1	$ 66.6