Investment in CyrusOne - Schedule of Related Party Transactions (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Operating costs and expenses:
Transaction-related compensation to CyrusOne employees		$ 20.0
Amounts receivable from and payable to CyrusOne
Dividends receivable	9.3	7.1
Receivable from CyrusOne	11.4		9.2
Payable to CyrusOne	0.7		0.5
CyrusOne [Member]
Related Party Transaction [Line Items]
Income Tax Receivable from Related Party	1.9		1.5
Revenue:
Services provided to CyrusOne	0.5	0.5
Operating costs and expenses:
Transaction-related compensation to CyrusOne employees	0	20.0
Charges for services provided by CyrusOne	2.3	1.5
Administrative services provided to CyrusOne	(0.1)	(0.1)
Total operating costs and expenses	2.2	21.4
Amounts receivable from and payable to CyrusOne
Accounts receivable	2.1		2.1
Dividends receivable	9.3		7.1
Receivable from CyrusOne	11.4		9.2
Accounts payable	0.7		0.5
Payable to CyrusOne	$ 0.7		$ 0.5