Real Estate (Real Estate Available and Held for Sale) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Real Estate Properties [Line Items]
Property transferred to held for sale, aggregate, carrying value	$ 31.3	$ 21.0	$ 17.9
Operating Properties
Real Estate Properties [Line Items]
Property transferred to held for sale, aggregate, carrying value	23.2	20.1	16.1
Net Lease
Real Estate Properties [Line Items]
Property transferred to held for sale, aggregate, carrying value	$ 8.1	$ 0.9	$ 1.8