Discontinued Operations - Summary of Revenue, Operating Profit, Income Tax Expense and After-tax Effects of Sales Treated as Discontinued Operations (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on sale of income-producing properties	$ 0.0	$ 0.0	$ 1.9	$ 0.0
Discontinued Operations | Real Estate Leasing
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from the sale of income-producing properties	0.0	0.0	0.0	70.1
Real estate leasing revenue	0.0	0.0	0.0	0.3
Total	0.0	0.0	0.0	70.4
Gain on sale of income-producing properties	0.0	0.0	0.0	55.9
Real estate leasing operating profit	0.0	0.0	0.0	0.3
Total operating profit before taxes	0.0	0.0	0.0	56.2
Income tax expense	0.0	0.0	0.0	21.9
Income from discontinued operations	$ 0.0	$ 0.0	$ 0.0	$ 34.3