Investment in CyrusOne - Schedule of Related Party Transactions (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended			3 Months Ended	9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Sep. 30, 2013 CyrusOne [Member]	Sep. 30, 2013 CyrusOne [Member]
Revenue:
Services provided to CyrusOne				$ 0.5	$ 1.6
Operating costs and expenses:
Transaction-related compensation to CyrusOne employees	20.0			0	20.0
Charges for services provided by CyrusOne				2.4	6.5
Administrative services provided to CyrusOne				(0.1)	(0.4)
Total operating costs and expenses				2.3	26.1
Amounts receivable from and payable to CyrusOne
Accounts receivable				0.9	0.9
Dividends receivable	7.1		0	7.1	7.1
Receivable from CyrusOne	8.0	0		8.0	8.0
Accounts payable				1.0	1.0
Payable to CyrusOne	$ 1.0	$ 0		$ 1.0	$ 1.0