Investment in CyrusOne - Schedule of Related Party Transactions (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Related Party Transaction [Line Items]
Income Tax Receivable from Related Party	$ 1.9		$ 1.9		$ 1.5
Operating costs and expenses:
Transaction-related compensation to CyrusOne employees				20.0
Amounts receivable from and payable to CyrusOne
Dividends receivable	6.0	7.1	6.0	7.1
Receivable from CyrusOne	8.0		8.0		9.2
Payable to CyrusOne	1.3		1.3		0.5
CyrusOne [Member]
Revenue:
Services provided to CyrusOne	0.4	0.5	1.3	1.6
Operating costs and expenses:
Transaction-related compensation to CyrusOne employees	0	0	0	20.0
Charges for services provided by CyrusOne	2.2	2.4	6.8	6.5
Administrative services provided to CyrusOne	(0.1)	(0.1)	(0.3)	(0.4)
Total operating costs and expenses	2.1	2.3	6.5	26.1
Amounts receivable from and payable to CyrusOne
Accounts receivable	2.0		2.0		2.1
Dividends receivable	6.0		6.0		7.1
Receivable from CyrusOne	8.0		8.0		9.2
Accounts payable	1.3		1.3		0.5
Payable to CyrusOne	$ 1.3		$ 1.3		$ 0.5