The stated principal amount of the debt instrument at time of issuance, which may vary from the carrying amount because of unamortized premium or discount.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 55

-Paragraph 8

-URI http://asc.fasb.org/extlink&oid=6584090&loc=d3e28878-108400

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Accounting Principles Board Opinion (APB)

-Number 21

-Paragraph 16, 20

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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

Fair Value Measurements Narrative (Details) (USD $) In Millions, unless otherwise specified							3 Months Ended
	Mar. 31, 2013 250 Million Senior Notes [Member] Senior Notes [Member]	Dec. 31, 2012 250 Million Senior Notes [Member] Senior Notes [Member]	Aug. 25, 2010 250 Million Senior Notes [Member] Senior Notes [Member]	Mar. 31, 2013 400 Million Senior Notes [Member] Senior Notes [Member]	Dec. 31, 2012 400 Million Senior Notes [Member] Senior Notes [Member]	Jun. 27, 2012 400 Million Senior Notes [Member] Senior Notes [Member]	Mar. 31, 2013 Fair Value, Inputs, Level 1 [Member] Mutual Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Defined Benefit Plan, Fair Value of Assets Sold							$ 0
Debt instrument face amount			250			400
Debt instrument fair value	$ 276.9	$ 271.6		$ 444.0	$ 442.0