Marketable Securities (Details) (USD $) In Millions	6 Months Ended
Sep. 30, 2011	Sep. 30, 2010	Mar. 31, 2011
Marketable Securities (Textual) [Abstract]
Available-for-sale Securities, Debt Maturities, within One Year, Amortized Cost	$ 89		$ 75
Available-for-sale Securities, Debt Maturities, after One Through Three Years, Amortized Cost	90		104
Proceeds from the sale of marketable securities	27	0
Realized gains and realized losses from sale of marketable securities	less than $1 million
U.S. Treasury and Government [Member]
Available-for-sale Securities
Aggregate Cost Basis	68		60
Gross Unrealized Gains	0		0
Gross Unrealized Losses	0		0
Investments	68		60
Municipal Notes [Member]
Available-for-sale Securities
Aggregate Cost Basis	1		2
Gross Unrealized Gains	0		0
Gross Unrealized Losses	0		0
Investments	1		2
Corporate Debt Securities [Member]
Available-for-sale Securities
Aggregate Cost Basis	110		117
Gross Unrealized Gains	0		0
Gross Unrealized Losses	0		0
Investments	110		117
Marketable Securities [Member]
Available-for-sale Securities
Aggregate Cost Basis	179		179
Gross Unrealized Gains	0		0
Gross Unrealized Losses	0		0
Investments	$ 179		$ 179

Available-for-sale Securities, Debt Maturities, after One Through Three Years, Amortized Cost.

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Realized gains and realized losses from sale of marketable securities.

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Schedule of Available for sale Securities.

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Schedule of Available for sale of Securities.

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This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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This item represents debt securities, at cost, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments, as defined), and fair value hedge accounting adjustments, if any, 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.

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This item represents the gross unrealized losses for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

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This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents investment securities as of the balance sheet date which may include marketable securities, derivative financial instruments, and investments accounted for under the equity method.

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