Leases - Components of Lease Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Operating lease income:
Variable lease income	$ 252.0	$ 252.8	$ 506.1	$ 505.7
Operating Lease, Variable Lease Income	15.7	17.4	30.5	35.1
Operating Lease, Lease Income	267.7	270.2	536.6	540.8
Finance lease income	1.6	2.7	3.4	5.5
Total lease income	269.3	272.9	540.0	546.3
Total operating lease income	$ 23.7	$ 20.6	$ 46.4	$ 44.3