Debt Debt - Credit Facility (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Jan. 24, 2013 Line of Credit [Member] CyrusOne LP [Member]
Line of Credit Facility [Line Items]
CyrusOne Credit Agreement				$ 225
Corporate Credit Agreement, Amount Outstanding	8.0		0
Line of Credit Facility, Remaining Borrowing Capacity	192.0
Receivables facility maximum borrowing capacity	120.0	105.0
Receivables facility amount outstanding	100.8		52.0
Letters of Credit Outstanding, Amount	5.2
Receivables facility maximum borrowing availability	$ 106.1
Accounts Receivable Facility, Renewal Term	364