Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplemental Cash Flow Information [Abstract]
Capitalized interest expense	$ 0.7	$ 0.7	$ 1.1
Interest	65.7	71.1	108.5
Income taxes, net of refunds	(12.9)	1.7	8.8
Accrual of CyrusOne dividends	0.0	1.1	2.1
Acquisition of property by assuming debt and other financing arrangements	17.3	12.0	5.8
Acquisition of property on account	$ 12.0	$ 23.8	$ 34.6