Senior Notes Senior Notes Narrative (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Debt Instrument, Face Amount	$ 1,500.0	$ 500.0
Unamortized Debt Issuance Expense	4.5	6.6
4.75% $1 Billion Senior Notes Due in August 2017 [Member]
Debt Instrument, Face Amount	1,000.0
Debt Instrument, Interest Rate, Stated Percentage	4.75%
6.75% $500 Million Senior Notes Due in June 2018 [Member]
Debt Instrument, Face Amount	500.0
Debt Instrument, Interest Rate, Stated Percentage	6.75%
Senior Notes [Member]
Unamortized Debt Issuance Expense	$ 17.2	$ 7.0

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.

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