Debt Debt - Credit Facility (Details) (USD $) In Millions, unless otherwise specified	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
Line of Credit Facility, Amount Outstanding	0
Line of Credit Facility, Remaining Borrowing Capacity	200.0
Receivables facility amount outstanding	54.0	52.0
Letters of Credit Outstanding, Amount	6.3
Receivables Facility Remaining Borrowing Capacity	32.4
Receivables facility maximum borrowing capacity	$ 92.7
Accounts Receivable Facility, Renewal Term	364