Debt Debt - Credit Facility (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2014	Jun. 30, 2013	Mar. 31, 2014	Dec. 31, 2013	Jun. 30, 2014 Tranche B Term Loan [Member]	Dec. 31, 2013 Tranche B Term Loan [Member]	Sep. 30, 2013 Tranche B Term Loan [Member]
Line of Credit Facility [Line Items]
Corporate Credit Agreement, Amount Outstanding	$ 0	$ 0
Line of Credit Facility, Remaining Borrowing Capacity	150.0	150.0
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
Debt Instrument, Face Amount						530.5	533.2	540.0
Long-Term Debt, Required Principal Payments	0.25%
Receivables facility amount outstanding	114.8	114.8			106.2
Letters of Credit Outstanding, Amount	5.2	5.2
Receivables Facility Remaining Borrowing Capacity	0	0
Receivables facility maximum borrowing availability	$ 120.0	$ 120.0
Accounts Receivable Facility, Renewal Term	364