Investment in CyrusOne - Schedule of Related Party Transactions (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
Operating costs and expenses:
Transaction-related compensation to CyrusOne employees	$ 20.0
Amounts receivable from and payable to CyrusOne
Dividends receivable	7.1		0
Receivable from CyrusOne	8.1	0
Payable to CyrusOne	22.5	0
CyrusOne [Member]
Revenue:
Services provided to CyrusOne	0.5
Operating costs and expenses:
Transaction-related compensation to CyrusOne employees	20.0
Charges for services provided by CyrusOne	1.5
Expense recoveries for services provided to CyrusOne	(0.1)
Total operating costs and expenses	21.4
Amounts receivable from and payable to CyrusOne
Accounts receivable	1.0
Dividends receivable	7.1
Receivable from CyrusOne	8.1
Accounts payable	2.9
Transaction-related compensation payable	19.6
Payable to CyrusOne	$ 22.5