Debt Debt - Credit Facility (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Jun. 30, 2014	Sep. 30, 2014	Sep. 30, 2013	Mar. 31, 2014	Dec. 31, 2013
Line of Credit Facility [Line Items]
Equity Method Investment Sold, Partnership Units		16.0
Proceeds from sale of CyrusOne equity method investment			$ 355.9	$ 0
Line of Credit Facility, Maximum Borrowing Capacity	150.0		150.0		200.0
Corporate Credit Agreement, Amount Outstanding	0		0
Line of Credit Facility, Remaining Borrowing Capacity	150.0		150.0
Long-Term Debt, Required Principal Payments	0.25%
Receivables facility amount outstanding	112.4		112.4			106.2
Letters of Credit Outstanding, Amount	5.2		5.2
Receivables Facility Remaining Borrowing Capacity	2.4		2.4
Receivables facility maximum borrowing availability	120.0		120.0
Accounts Receivable Facility, Renewal Term	364
Tranche B Term Loan [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Face Amount	$ 529.2		$ 529.2	$ 540.0		$ 533.2