Marketable Securities (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
Dec. 31, 2011	Dec. 31, 2010	Mar. 31, 2011
Marketable Securities (Textual) [Abstract]
Available-for-sale Securities, Debt Maturities, within One Year, Amortized Cost	$ 102		$ 75
Available-for-sale Securities, Debt Maturities, after One Through Three Years, Amortized Cost	79		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	55		60
Gross Unrealized Gains	0		0
Gross Unrealized Losses	0		0
Investments	55		60
Municipal Notes [Member]
Available-for-sale securities
Aggregate Cost Basis	2		2
Gross Unrealized Gains	0		0
Gross Unrealized Losses	0		0
Investments	2		2
Corporate Debt Securities [Member]
Available-for-sale securities
Aggregate Cost Basis	124		117
Gross Unrealized Gains	0		0
Gross Unrealized Losses	0		0
Investments	124		117
Marketable Securities [Member]
Available-for-sale securities
Aggregate Cost Basis	181		179
Gross Unrealized Gains	0		0
Gross Unrealized Losses	0		0
Investments	$ 181		$ 179

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

No definition available.

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- Definition

Realized gains and realized losses from sale of marketable securities.

+ References

No definition available.

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- Definition

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.

+ References

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-Publisher FASB

-Name FASB Staff Position (FSP)

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-Paragraph 7

-Footnote 2

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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

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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 19

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-Publisher FASB

-Name Accounting Standards Codification

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-Section S99

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- Definition

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.

+ References

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-Publisher FASB

-Name FASB Staff Position (FSP)

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-Paragraph 7

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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.

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-Publisher FASB

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-Number 115

-Paragraph 20

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- Definition

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

+ References

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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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-Paragraph 2

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- Definition

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.

+ References

No definition available.

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- Definition

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.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

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-Name Accounting Standards Codification

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 7

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- Definition

The cash inflow associated with the sale of debt securities classified as available-for-sale securities.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

-Glossary Investing Activities

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