| Cover Page - USD ($) $ in Billions | 12 Months Ended | ||
| Dec. 31, 2020 | Feb. 12, 2021 | Jun. 30, 2020 | |
| Document Information [Line Items] | |||
| Document Type | 10-K/A | ||
| Document Annual Report | true | ||
| Document Period End Date | Dec. 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 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 | ||
| ICFR Auditor Attestation Flag | true | ||
| Entity Shell Company | false | ||
| Entity Public Float | $ 8.5 | ||
| Entity Common Stock, Shares Outstanding | 120,460,690 | ||
| Entity Central Index Key | 0001553023 | ||
| Current Fiscal Year End Date | --12-31 | ||
| Document Fiscal Year Focus | 2020 | ||
| Document Fiscal Period Focus | FY | ||
| Amendment Flag | true | ||
| Amendment Description | This Amendment No. 1 on Form 10-K/A (“Amendment No. 1”) is being filed for the sole purpose of including the conformed signature of our Independent Registered Public Accounting Firm on Exhibit 23.1 (Consent of Independent Registered Public Accounting Firm), which was inadvertently omitted from Exhibit 23.1 in the original filing of the Form 10-K.Except as expressly noted above, this Amendment No. 1 does not modify or update in any way disclosures made in the original filing. | ||
| Common Stock [Member] | |||
| 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 |
