| Cover - USD ($) $ in Billions | 12 Months Ended | ||
| Dec. 31, 2021 | Mar. 22, 2022 | Jun. 30, 2021 | |
| Document Information [Line Items] | |||
| Document Type | 10-K/A | ||
| Amendment Flag | false | ||
| Document Annual Report | true | ||
| Document Transition Report | false | ||
| Document Period End Date | Dec. 31, 2021 | ||
| Document Fiscal Period Focus | FY | ||
| Document Fiscal Year Focus | 2021 | ||
| Current Fiscal Year End Date | --12-31 | ||
| Entity File Number | 001-35789 | ||
| Entity Registrant Name | CyrusOne Inc. | ||
| Entity Central Index Key | 0001553023 | ||
| Entity Tax Identification Number | 46-0691837 | ||
| Entity Incorporation, State or Country Code | MD | ||
| 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 Well-known Seasoned Issuer | Yes | ||
| Entity Voluntary Filers | No | ||
| 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 Public Float | $ 8.9 | ||
| Entity Common Stock, Shares Outstanding | 131,149,400 | ||
| ICFR Auditor Attestation Flag | true | ||
| Auditor Name | Deloitte & Touche LLP | ||
| Auditor Location | Dallas, Texas | ||
| Auditor Firm ID | 34 | ||
| Common Stock | |||
| Document Information [Line Items] | |||
| Title of 12(b) Security | Common Stock, $.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 |
