Long Term Debt (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
Jun. 30, 2012	Jun. 30, 2011
Long Term Debt (Textuals)
Issuance of long-term debt	$ 0	$ 420.0
Extinguishment of Debt, Amount		450
Series B [Member]
Long Term Debt (Textuals)
Issuance of long-term debt		420.0
Series B Senior Notes due January 19 2031 [Member]
Long Term Debt (Textuals)
Issuance of long-term debt		205.0
Interest rate on Long Term Debt		4.673%
Series B Senior Notes due January 19 2041 [Member]
Long Term Debt (Textuals)
Issuance of long-term debt		$ 215.0
Interest rate on Long Term Debt		5.848%

The cash inflow from a debt initially having maturity due after one year or beyond the operating cycle, if longer.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 19

-Subparagraph b

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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

-Glossary Financing Activities

-URI http://asc.fasb.org/extlink&oid=6513228

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 18

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 14

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3255-108585

Name:	us-gaap_ProceedsFromIssuanceOfLongTermDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration