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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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

Reference 2: 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 3: 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

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

Long-Term Debt (Schedule Of Principal Amount, Effective Interest Rate And Maturity Date Of Debentures And Senior Notes) (Details) (USD $)	1 Months Ended	12 Months Ended
	Jan. 23, 2011	Dec. 31, 2011	Dec. 31, 2010
6.6% Senior Notes, Due 2018 [Member]
Debt Instrument [Line Items]
Principal Amount		$ 300,000,000
Effective Interest Rate		6.81%
Maturity date		April 15, 2018	April 15, 2018
7% Debentures, Due 2025 [Member]
Debt Instrument [Line Items]
Principal Amount		125,000,000
Effective Interest Rate		7.12%
Maturity date		December 1, 2025	December 1, 2025
6.25% Senior Notes, Due 2037 [Member]
Debt Instrument [Line Items]
Principal Amount		$ 250,000,000
Effective Interest Rate		6.45%
Maturity date	2037	May 1, 2037	May 1, 2037