Summary of Significant Accounting Polices and Adoption of New Accounting Pronouncements (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Mar. 31, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Other assets	$ (253.4)			$ (253.4)		$ (263.1)
Unconsolidated investments	613.7			613.7		519.3
Income from unconsolidated investments	10.9	$ 10.8		36.9	$ 39.8
Accounting Standards Update 2014-09 [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Income from unconsolidated investments	$ 6.9			$ 17.2
Restatement Adjustment [Member] | Accounting Standards Update 2014-09 [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Other assets						32.9
Unconsolidated investments						$ 32.9
Income from unconsolidated investments		(2.7)	$ (2.7)		3.9
Investment management, property services and research fees (includes $3.43, $0.3, $6.3 and $10.0 of related party fees)		$ (2.6)			$ 3.9