| **Financing Arrangement**       | 9 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             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| **Debt Instruments [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            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| Financing Arrangement           | ) FINANCING ARRANGEMENTS0.75% Convertible Senior Notes Due 2016In July 2011, we issued $632.5 million aggregate principal amount of 0.75% Convertible Senior Notes due 2016 (the “Notes”). The Notes are senior unsecured obligations which pay interest semiannually in arrears at a rate of 0.75 percent per annum on January 15 and July 15 of each year, beginning on January 15, 2012 and will mature on July 15, 2016, unless earlier purchased or converted in accordance with their terms prior to such date. The Notes are senior in right of payment to any unsecured indebtedness that is expressly subordinated in right of payment to the Notes.The Notes are convertible into cash and shares of our common stock based on an initial conversion value of 31.5075 shares of our common stock per $1,000 principal amount of Notes (equivalent to an initial conversion price of approximately $31.74 per share). Upon conversion of the Notes, holders will receive cash up to the principal amount of each Note, and any excess conversion value will be delivered in shares of our common stock. Prior to April 15, 2016, the Notes are convertible only if (1) the last reported sale price of the common stock for at least 20 trading days (whether or not consecutive) during the period of 30 consecutive trading days ending on the last trading day of the immediately preceding fiscal quarter is greater than or equal to 130 percent of the conversion price ($41.26 per share) on each applicable trading day; (2) during the five business day period after any ten consecutive trading day period in which the trading price per $1,000 principal amount of notes falls below 98 percent of the last reported sale price of our common stock multiplied by the conversion rate on each trading day; or (3) specified corporate transactions, including a change in control, occur. On or after April 15, 2016, a holder may convert any of its Notes at any time prior to the close of business on the second scheduled trading day immediately preceding the maturity date. The conversion rate is subject to customary anti-dilution adjustments (for example, certain dividend distributions or tender or exchange offer of our common stock), but will not be adjusted for any accrued and unpaid interest. The Notes are not redeemable prior to maturity except for specified corporate transactions and events of default, and no sinking fund is provided for the Notes. The Notes do not contain any financial covenants.We separately account for the liability and equity components of the Notes. The carrying amount of the equity component representing the conversion option is equal to the fair value of the Convertible Note Hedge, as described below, which is a substantially identical instrument and was purchased on the same day as the Notes. The carrying amount of the liability component was determined by deducting the fair value of the equity component from the par value of the Notes as a whole, and represents the fair value of a similar liability that does not have an associated convertible feature. A liability of $525 million as of the date of issuance was recognized for the principal amount of the Notes representing the present value of the Notes’ cash flows using a discount rate of 4.54 percent. The excess of the principal amount of the liability component over its carrying amount is amortized to interest expense over the term of the Notes using the effective interest method. The equity component is not remeasured as long as it continues to meet the conditions for equity classification.In accounting for $15 million of issuance costs related to the Notes issuance, we allocated $13 million to the liability component and $2 million to the equity component. Debt issuance costs attributable to the liability component are being amortized to interest expense over the term of the Notes, and issuance costs attributable to the equity component were netted with the equity component in additional paid-in capital.The carrying values of the liability and equity components of the Notes are reflected in our Condensed Consolidated Balance Sheet as follows (in millions):   As ofDecember 31, 2012 As of March 31, 2012Principal amount of Notes$633 $633Unamortized discount of the liability component(79) (94)Net carrying amount of Notes$554 $539Equity component, net$105 $105As of December 31, 2012, the remaining life of the Notes is 3.5 years.Convertible Note Hedge and Warrants IssuanceIn addition, in July 2011, we entered into privately negotiated convertible note hedge transactions (the “Convertible Note Hedge”) with certain counterparties to reduce the potential dilution with respect to our common stock upon conversion of the Notes. The Convertible Note Hedge, subject to customary anti-dilution adjustments, provides us with the option to acquire, on a net settlement basis, approximately 19.9 million shares of our common stock at a strike price of $31.74, which corresponds to the conversion price of the Notes and is equal to the number of shares of our common stock that notionally underlie the Notes. As of December 31, 2012, we have not purchased any shares under the Convertible Note Hedge. We paid $107 million for the Convertible Note Hedge, which was recorded as an equity transaction.Separately, in July 2011 we also entered into privately negotiated warrant transactions with the certain counterparties whereby we sold to independent third parties warrants (the “Warrants”) to acquire, subject to customary anti-dilution adjustments that are substantially the same as the anti-dilution provisions contained in the Notes, up to 19.9 million shares of our common stock (which is also equal to the number of shares of our common stock that notionally underlie the Notes), with a strike price of $41.14. The Warrants could have a dilutive effect with respect to our common stock to the extent that the market price per share of our common stock exceeds $41.14 on or prior to the expiration date of the Warrants. We received proceeds of $65 million from the sale of the Warrants.Credit FacilityOn August 30, 2012, we entered into a $500 million3.5 years senior unsecured revolving credit facility with a syndicate of banks. The credit facility terminates on February 29, 2016 and contains an option to arrange with existing lenders and/or new lenders for them to provide up to an aggregate of $250 million in additional commitments for revolving loans. Proceeds of loans made under the credit facility may be used for general corporate purposes.The loans bear interest, at our option, at the base rate plus an applicable spread or an adjusted LIBOR rate plus an applicable spread, in each case with such spread being determined based on our consolidated leverage ratio for the preceding fiscal quarter. We are also obligated to pay other customary fees for a credit facility of this size and type. Interest is due and payable in arrears quarterly for loans bearing interest at the base rate and at the end of an interest period (or at each three month interval in the case of loans with interest periods greater than three months) in the case of loans bearing interest at the adjusted LIBOR rate. Principal, together with all accrued and unpaid interest, is due and payable on February 29, 2016. The credit agreement contains customary affirmative and negative covenants, including covenants that limit or restrict our ability to, among other things, incur subsidiary indebtedness, grant liens, dispose of all or substantially all assets and pay dividends or make distributions, in each case subject to customary exceptions for a credit facility of this size and type. We are also required to maintain compliance with a capitalization ratio and maintain a minimum level of total liquidity and a minimum level of domestic liquidity.The credit agreement contains customary events of default, including among others, non-payment defaults, covenant defaults, bankruptcy and insolvency defaults and a change of control default, in each case, subject to customary exceptions for a credit facility of this size and type. The occurrence of an event of default could result in the acceleration of the obligations under the credit agreement, an obligation by any guarantors to repay the obligations in full and an increase in the applicable interest rate.As of December 31, 2012, no amounts were outstanding under the credit facility. During the three months ended September 30, 2012, we paid $2 million of debt issuance costs in connection with obtaining this credit facility. These costs are deferred and are being amortized to interest expense over the 3.5 years term of the credit facility.   Interest expense recognized related to our financing arrangements are as follows (in millions):  Three Months EndedDecember 31, Nine Months EndedDecember 31, 2012 2011 2012 2011Amortization of debt discount$5 $5 $15 $9Amortization of debt issuance costs— — 2 1Coupon interest expense1 1 3 2Other interest expense1 1 1 1Total interest expense$7 $7 $21 $13 |

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| - Definition
The entire disclosure for long-term debt.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 22 -Article 5
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