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Financial Instruments (Fair Value Of Marketable Equity Securities Schedule) (Details) (USD $)
In Millions
Sep. 30, 2011
Mar. 31, 2011
Financial Instruments [Line Items]  
Fair Value$ 214$ 161[1]
Marketable Equity Securities [Member]
  
Financial Instruments [Line Items]  
Adjusted Cost3232
Gross Unrealized Gains182129
Gross Unrealized Losses  
Fair Value$ 214$ 161
[1]Derived from audited consolidated financial statements.