Investments in Marketable Securities (Naratives) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Mar. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Total, fair value	$ 4,659	$ 4,822

For an unclassified balance sheet, this item represents investments in debt and equity securities which are categorized neither as held-to-maturity nor trading.

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+ Details