Long-Term Debt (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2013
Credit agreement
Long-Term Debt
Borrowing capacity	$ 1,653.0
Revolving credit facility due July 2016
Long-Term Debt
Borrowing capacity	1,128.0
Additional borrowing capacity available	47.0
Increase in capacity	20.0
Revolving credit facility due November 2014
Long-Term Debt
Borrowing capacity	$ 525.0

Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19(b),22(b))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

Name:	us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant