Condensed Consolidated Statement of Equity / Partnership Capital (USD $) In Millions, except Share data, unless otherwise specified	Total	Additional Paid In Capital USD ($)	Non- controlling Interest USD ($)	Predecessor [Member] USD ($)	Predecessor [Member] CyrusOne LP [Member] USD ($)	Predecessor [Member] Common Stock Issued USD ($)	Predecessor [Member] Additional Paid In Capital USD ($)	Predecessor [Member] Accumulated Deficit USD ($)	Predecessor [Member] Partnership Capital USD ($)	Predecessor [Member] Total Shareholders' Equity/ Parent’s Net Investment USD ($)	Predecessor [Member] Non- controlling Interest USD ($)	Successor [Member] USD ($)	Successor [Member] CyrusOne LP [Member] USD ($)	Successor [Member] Common Stock Issued USD ($)	Successor [Member] Additional Paid In Capital USD ($)	Successor [Member] Accumulated Deficit USD ($)	Successor [Member] Partnership Capital USD ($)	Successor [Member] Total Shareholders' Equity/ Parent’s Net Investment USD ($)	Successor [Member] Non- controlling Interest USD ($)	Successor [Member] Partnership Units CyrusOne LP [Member]	Successor [Member] Partnership Capital [Member] CyrusOne LP [Member] USD ($)
Beginning Balance at Dec. 31, 2012				$ 500.1		$ 0	$ 7.1	$ 0	$ 493.0	$ 500.1	$ 0
Beginning Balance (in shares) at Dec. 31, 2012						0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)				(20.2)	(20.2)				(20.2)	(20.2)
Other contributions from Parent				1.3					1.3	1.3
Contributions from Parent—Transaction compensation expense reimbursement				19.6					19.6	19.6
Noncontrolling interest effective				0			(7.1)		(493.7)	(500.8)	500.8
Common stock issued				337.1		0.2	336.9			337.1
Common stock issued (in shares)						19,000,000
Common stock issued to CBI in exchange for operating partnership units				0
Common stock issued to CBI in exchange for operating partnership units (in shares)						1,500,000
Common stock issued to CBI in exchange for settlement of IPO costs paid by CBI				0			7.1			7.1	(7.1)
Common stock issued to CBI in exchange for settlement of IPO costs paid by CBI (in shares)						400,000
Stock issuance costs				(9.5)			(9.5)			(9.5)
Restricted shares issued (in shares)				0
Restricted shares issued						1,200,000
Ending Balance at Jan. 23, 2013
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)												(11.8)	(11.8)			(11.8)		(11.8)
Noncontrolling interest allocated net loss												7.8				7.8		7.8	(7.8)
Restricted shares issued under long-term incentive plans												4.9			4.9			4.9
Dividends, $0.32 and $0.42 per share												(31.1)				(10.2)		(10.2)	(20.9)
Ending Balance at Sep. 30, 2013												790.4		0.2	339.4	(14.2)	0	325.4	465.0
Ending Balance (in shares) at Sep. 30, 2013														22,100,000
Beginning Balance at Jun. 30, 2013
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)												(2.2)	(2.2)
Noncontrolling interest allocated net loss												1.4
Ending Balance at Sep. 30, 2013												790.4		0.2			0
Ending Balance (in shares) at Sep. 30, 2013														22,100,000
Beginning Balance at Dec. 31, 2013												777.6	777.6	0.2	340.7	(18.9)	0	322.0	455.6		777.6
Beginning Balance (in shares) at Dec. 31, 2013														22,000,000						64,600,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)												(2.7)	(2.7)			(2.7)		(2.7)	0
Common stock issued												355.9		0.2	355.7			355.9
Common stock issued (in shares)														16,000,000
Stock issuance costs												(1.3)			(1.3)			(1.3)
Restricted shares issued (in shares)												0
Restricted shares issued														700,000
Noncontrolling interest allocated net loss												1.9				1.9		1.9	(1.9)
Restricted shares issued under long-term incentive plans												7.6			7.6			7.6
Redemption of noncontrolling interest		(189.0)	(166.9)									(355.9)			(189.0)			(189.0)	(166.9)
Dividends, $0.32 and $0.42 per share												(41.2)				(21.1)		(21.1)	(20.1)
Ending Balance at Sep. 30, 2014												740.0	740.0	0.4	513.7	(40.8)	0	473.3	266.7
Ending Balance (in shares) at Sep. 30, 2014														38,700,000
Beginning Balance at Jun. 30, 2014
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)												0.2	0.2								(2.7)
Common stock issued (in shares)																				700,000
Noncontrolling interest allocated net loss												(0.1)
Restricted shares issued under long-term incentive plans																					7.6
Partnership units purchased by CyrusOne Inc.																					355.9
Partnership units purchased by CyrusOne Inc. (in shares)																				16,000,000
Partnership units sold by CBI																					(355.9)
Partnership units sold by CBI (in shares)																				(16,000,000)
Distributions to CyrusOne Inc.																					(1.3)
Dividends, $0.32 and $0.42 per share																					(41.2)
Ending Balance at Sep. 30, 2014												$ 740.0	$ 740.0				$ 0				$ 740.0
Ending Balance (in shares) at Sep. 30, 2014																				65,300,000