Formation - Additional Information (Detail) $ / shares in Units, $ in Millions							9 Months Ended
	Jul. 01, 2015 USD ($) data_center area shares	Jun. 26, 2015 USD ($) $ / shares shares	Apr. 07, 2015 USD ($) $ / shares shares	Jun. 25, 2014 USD ($) $ / shares shares	Jan. 24, 2013 USD ($) shares	Nov. 20, 2012 shares	Sep. 30, 2015 USD ($) $ / shares shares	Sep. 30, 2014 USD ($) shares	Dec. 31, 2014 shares	Jun. 26, 2014	Dec. 31, 2013 shares
Business Formation [Line Items]
Net partnership units issued to CyrusOne Inc.					400,000
Partnership units exchanged					1,500,000
Proceeds from partnership units exchanged					1,500,000
Number of common shares issued to directors and employees					1,100,000
Shares purchased of operating partnership's units				16,000,000
Share price (in dollars per share) | $ / shares							$ 32.66
Number Of data center facilities under capital leases | data_center	4
Work area recovery facilities, new york | area	2
Common stock issued (in shares)							66,245,906		38,651,517
Issuance of common stock | $							$ 799.3	$ 355.9
IPO
Business Formation [Line Items]
Net partnership units issued to CyrusOne Inc.				16,000,000	19,000,000
Proceeds from issuance of initial public offering, net | $		$ 373.3	$ 426.0	$ 355.9	$ 337.1		373.3
Share price (in dollars per share) | $ / shares				$ 23.25
Amount received from initial public offering of common stock, net of underwriter's discount | $		203.0		$ 371.7			203.0
Underwriting costs | $		$ 16.6	$ 17.8	$ 15.8			16.6
Over-Allotment Option
Business Formation [Line Items]
Net partnership units issued to CyrusOne Inc.				2,100,000
Limited Partner
Business Formation [Line Items]
Partnership units issued to CyrusOne Inc.						123,700,000
Reverse unit split executed					2.8
Operating partnership units owned					44,100,000
Issuance of common stock | $							799.3
Cyrus One Inc | IPO
Business Formation [Line Items]
Common stock issued (in shares)		13,000,000
Initial public offering, share over-allotment		1,700,000
Shares issued, price per share | $ / shares		$ 30.00
Issuance of common stock | $		$ 389.9
CyrusOne Inc. and CyrusOne GP
Business Formation [Line Items]
Combined interest held on completion of transactions					33.90%
Shares purchased of operating partnership's units					21,900,000
Purchase of operating partnership's units | $					$ 337.1
Cincinnati Bell Inc.
Business Formation [Line Items]
Shares purchased of operating partnership's units	6,000,000		14,300,000
Remaining combined interest held					66.10%
Ownership percentage								40.80%
CyrusOne LP | IPO
Business Formation [Line Items]
Amount received from initial public offering of common stock, net of underwriter's discount | $	$ 170.3
Cervalis | CyrusOne LP
Business Formation [Line Items]
Issuance of common stock | $							$ 170.3
Outstanding partnership units							6,000,000
Maximum | Cincinnati Bell Inc.
Business Formation [Line Items]
Remaining combined interest held										50.00%
Maximum | Cervalis | CyrusOne LP
Business Formation [Line Items]
Business acquisition, transaction costs | $	$ 400.0
Partnership Units | CyrusOne LP
Business Formation [Line Items]
Net partnership units issued to CyrusOne Inc.							300,000	700,000
Common stock, shares, outstanding							72,600,000	65,300,000	65,300,000		64,600,000
6.375% Senior Notes Due 2022
Business Formation [Line Items]
Stated interest rate						6.375%	6.375%		6.375%
Senior Notes | 6.375% Senior Notes Due 2022 | Cyrus One Lp And Cyrus One Finance Corp
Business Formation [Line Items]
Stated interest rate						6.375%	6.375%
Cyrus One Inc | Cincinnati Bell Inc.
Business Formation [Line Items]
Ownership percentage							2.60%
Cyrus One Lp And Cyrus One Finance Corp | Cincinnati Bell Inc.
Business Formation [Line Items]
Ownership percentage							11.30%
CyrusOne LP | Cincinnati Bell Inc.
Business Formation [Line Items]
Ownership percentage							8.70%
Common Stock Issued | IPO
Business Formation [Line Items]
Net partnership units issued to CyrusOne Inc.		13,000,000	14,300,000
Share price (in dollars per share) | $ / shares		$ 30.00	$ 31.12
Amount received from initial public offering of common stock, net of underwriter's discount | $		$ 389.9	$ 443.8
Common Stock Issued | Over-Allotment Option
Business Formation [Line Items]
Net partnership units issued to CyrusOne Inc.		1,700,000	1,900,000