Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Capitalized interest expense	$ 1.1	$ 0.8	$ 0.6
Interest	108.5	153.1	179.5
Income taxes, net of refunds	8.8	9.1	2.8
Noncash Investing and Financing Items [Abstract]
Investment in CyrusOne resulting from deconsolidation	0.0	0.0	509.7
Acquisition of property by assuming debt and other financing arrangements	5.8	4.7	7.6
Acquisition of property on account	34.6	24.8	13.3
CyrusOne [Member]
Noncash Investing and Financing Items [Abstract]
Accrual of CyrusOne dividends	$ 2.1	$ 6.0	$ 7.1