Cover Page - shares	3 Months Ended
	Mar. 31, 2020	Apr. 24, 2020
Document Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2020
Document Transition Report	false
Entity File Number	001-35789
Entity Registrant Name	CyrusOne Inc.
Entity Incorporation, State or Country Code	MD
Entity Tax Identification Number	46-0691837
Entity Address, Address Line One	2850 N. Harwood Street
Entity Address, Address Line Two	Suite 2200
Entity Address, City or Town	Dallas
Entity Address, State or Province	TX
Entity Address, Postal Zip Code	75201
City Area Code	972
Local Phone Number	350-0060
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		115,199,834
Entity Central Index Key	0001553023
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q1
Amendment Flag	false
Common Stock, $0.01 par value
Document Information [Line Items]
Title of 12(b) Security	Common Stock, $0.01 par value
Trading Symbol	CONE
Security Exchange Name	NASDAQ
1.450% Senior Notes due 2027
Document Information [Line Items]
Title of 12(b) Security	1.450% Senior Notes due 2027
Trading Symbol	CONE27
Security Exchange Name	NASDAQ