Available-For-Sale Securities (Amount Of Available-For-Sale Debt Securities By Maturity Periods) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012
Schedule of Available-for-Sale Securities [Line Items]
Available-for-sale debt securities, Less than one year	$ 15
Available-for-sale debt securities, 1-5 years	140
Available-for-sale debt securities, 6-10 years	173
Available-for-sale debt securities, 11-15 years	49
Available-for-sale debt securities, 16-20 years	15
Available-for-sale debt securities, Over 20 years	236
Available-for-sale debt securities, Total	628
Rabbi Trust Fund [Member]
Schedule of Available-for-Sale Securities [Line Items]
Available-for-sale debt securities, Less than one year	0
Available-for-sale debt securities, 1-5 years	53
Available-for-sale debt securities, 6-10 years	29
Available-for-sale debt securities, 11-15 years	15
Available-for-sale debt securities, 16-20 years	3
Available-for-sale debt securities, Over 20 years	51
Available-for-sale debt securities, Total	$ 151

This item represents the fair value of debt securities which are expected to mature after five years and through ten years from the balance sheet date and which are categorized neither as held-to-maturity nor trading securities.

+ References+ Details

This item represents the fair value of debt securities which are expected to mature after one year and through five years from the balance sheet date and which are categorized neither as held-to-maturity nor trading securities.

+ References+ Details

- Definition

This item represents the fair value of debt securities which are expected to mature within one year of the balance sheet date and which are categorized neither as held-to-maturity nor trading securities.

+ References+ Details

- Definition

For an unclassified balance sheet, total of debt securities categorized neither as held-to-maturity nor trading.

+ References

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

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

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Reference 4: http://www.xbrl.org/2003/role/presentationRef

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Reference 5: http://www.xbrl.org/2003/role/presentationRef

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Reference 6: http://www.xbrl.org/2003/role/presentationRef

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-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 7: http://www.xbrl.org/2003/role/presentationRef

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Reference 8: http://www.xbrl.org/2003/role/presentationRef

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-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 9: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

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-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 10: http://www.xbrl.org/2003/role/presentationRef

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+ Details