Investment in CyrusOne (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended				3 Months Ended	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012	Dec. 31, 2011	Jun. 30, 2013 CyrusOne [Member]	Jun. 30, 2013 CyrusOne [Member]	Jan. 24, 2013 CyrusOne [Member]
Schedule of Equity Method Investments [Line Items]
Loss from CyrusOne	$ (4.7)	$ 0	$ (6.6)	$ 0
Investment owned in CyrusOne Inc., Balance, Shares	1.9		1.9
Investment owned in CyrusOne LP, Balance, Partnership Units	42.6		42.6
Total ownership interests in CyrusOne, Percentage	69.00%		69.00%
Equity Method Investments, Fair Value Disclosure	922.4		922.4		0
Dividends received from CyrusOne	7.0		7.0	0
Dividends Payable, Amount Per Share							$ 0.16	$ 0.16
Equity Method Investment, Summarized Financial Information, Assets [Abstract]
Cash	5.5	4.1	5.5	4.1	23.6	73.7			12.2
Receivables	148.3		148.3		199.0				41.5
Other current assets	1.4		1.4		11.6				13.4
Property, plant and equipment	879.0		879.0		1,587.4				736.2
Goodwill and intangibles									377.7
Other noncurrent assets	41.1		41.1		86.3				44.0
Total assets									1,225.0
Equity Method Investment, Summarized Financial Information, Liabilities [Abstract]
Current portion of long-term debt	7.2		7.2		13.4				6.3
Accounts payable	103.1		103.1		135.6				29.4
Unearned revenue and customer deposits	32.5		32.5		51.2				24.1
Other current liabilities	33.7		33.7		40.2				12.9
Long-term debt	2,183.0		2,183.0		2,676.0				550.3
Other noncurrent liabilities	73.8		73.8		176.5				92.3
Total liabilities									715.3
Equity Method Investment, Financial Statement, Reported Amounts [Abstract]
Net assets			509.7	0
Equity Method Investment, Summarized Financial Information, Income Statement [Abstract]
Revenue							63.6	108.6
Operating income	46.8	65.2	66.0	146.2			5.6	11.4
Net loss							$ (6.8)	$ (9.6)