Related Party Transactions - Narrative (Details) - USD ($) shares in Millions, $ in Millions		12 Months Ended
	Dec. 31, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Related Party Transaction [Line Items]
Dividends payable	$ 24.4	$ 24.4	$ 14.3
Common stock issued (in shares)		0.2
CyrusOne LP
Related Party Transaction [Line Items]
Dividends payable	$ 2.0	$ 2.0
Common stock issued (in shares)	6.3
Bosselaw
Related Party Transaction [Line Items]
Expenses to related party				$ 1.6
Jones Lang LaSalle
Related Party Transaction [Line Items]
Expenses to related party		$ 1.1	1.0	1.5
Skadden
Related Party Transaction [Line Items]
Expenses to related party			$ 1.1	$ 0.2