Condensed Consolidated Statements of Equity / Partnership Capital - USD ($) shares in Millions, $ in Millions	Total	Common Stock Issued	Additional Paid In Capital	Accumulated Deficit	Accumulated Other Comprehensive Loss	Total Shareholders' Equity/ Parent’s Net Investment	Non- controlling Interest	CyrusOne LP	CyrusOne LP Partnership Units	CyrusOne LP Partnership Capital
Beginning Balance (in shares) at Dec. 31, 2013		22.0							64.6
Beginning Balance at Dec. 31, 2013	$ 777.6	$ 0.2	$ 340.7	$ (18.9)		$ 322.0	$ 455.6			$ 777.6
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(2.7)			(2.7)		(2.7)		$ (2.7)		(2.7)
Noncontrolling interest allocated net loss	1.9			1.9		1.9	(1.9)
Stock issuance costs	(1.3)		(1.3)			(1.3)
Stock based compensation (in shares)		0.7
Stock based compensation	7.6		7.6			7.6
Issuance of common stock and Net parternship units issued to CyrusOne Inc. (shares)		16.0							0.7
Issuance of common stock and Net parternship units issued to CyrusOne Inc.	355.9	$ 0.2	355.7			355.9
Redemption of noncontrolling interest	(355.9)		(189.0)			(189.0)	(166.9)
Dividends and distributions	(41.2)		0.0	(21.1)		(21.1)	(20.1)
Compensation expense of CyrusOne Inc. allocated to operating partnership										7.6
Distributions to CyrusOne Inc.										(1.3)
Partnership units purchased by CyrusOne Inc. (in shares)									16.0
Partnership units purchased by CyrusOne Inc.										355.9
Partnership units sold by CBI (in shares)									(16.0)
Partnership units sold by CBI										(355.9)
Partnership distributions										(41.2)
Foreign currency translation adjustments	0.0							0.0
Ending Balance (in shares) at Sep. 30, 2014		38.7							65.3
Ending Balance at Sep. 30, 2014	740.0	$ 0.4	513.7	(40.8)		473.3	266.7			740.0
Beginning Balance (in shares) at Dec. 31, 2014		38.7							65.3
Beginning Balance at Dec. 31, 2014	717.0	$ 0.4	516.5	(55.9)	$ (0.3)	460.7	256.3	717.0		717.0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(19.0)			(19.0)		(19.0)		(19.0)		(19.0)
Noncontrolling interest allocated net loss	4.6			4.6		4.6	(4.6)
Stock issuance costs	(0.8)		(0.8)			(0.8)
Stock based compensation (in shares)		0.3
Stock based compensation	10.5		10.5			10.5
Issuance of common stock and Net parternship units issued to CyrusOne Inc. (shares)		27.3							0.3
Issuance of common stock and Net parternship units issued to CyrusOne Inc.	799.3	$ 0.2	799.1			799.3
Redemption of noncontrolling interest	(596.4)		(412.2)			(412.2)	(184.2)
Dividends and distributions	(68.3)			(54.0)		(54.0)	(14.3)
Common stock repurchases	(0.8)		(0.8)			(0.8)
Compensation expense of CyrusOne Inc. allocated to operating partnership										10.5
Distributions to CyrusOne Inc.										(0.8)
Partnership units purchased by CyrusOne Inc. (in shares)									27.3
Partnership units purchased by CyrusOne Inc.										798.5
Partnership units sold by CBI (in shares)									(20.3)
Partnership units sold by CBI										(596.4)
Partnership distributions										(68.3)
Foreign currency translation adjustments	(0.4)				(0.4)	(0.4)	0.0	(0.4)		(0.4)
Ending Balance (in shares) at Sep. 30, 2015		66.3							72.6
Ending Balance at Sep. 30, 2015	$ 841.1	$ 0.6	$ 912.3	$ (124.3)	$ (0.7)	$ 787.9	$ 53.2	$ 841.1		$ 841.1