Amount of decrease in interest expense in effect as of the balance sheet date from change in amount of fair value of derivative.

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Non-cash interest expense related to convertible debt instruments which has been recognized for the period from amortization of the debt discount.

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The approximate initial (at the debt of date issuance) conversion price per share of the conversion feature embedded in the debt instrument.

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The amount of debt discount from estimated fair value of the liability component of the debentures at the issuance date.

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The principal amount of convertible debt instrument that is used as the conversion unit to determine the number of shares the holder of the debt instrument can convert the debt into.

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The initial ratio applied to the debt for purposes of determining the number of shares of the equity security into which the debt will be converted.

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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. Fair value of junior subordinated convertible debenture at the balance sheet date.

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The portion of the carrying value of convertible subordinated debt as of the balance sheet date that is scheduled to be repaid after one year or beyond the normal operating cycle if longer. This form of debt can be exchanged for a specified amount of another security, typically the entity's common stock, at the option of the issuer or the holder, and places a lender in a lien position behind debt having a higher priority of repayment in liquidation of the entity's assets.

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The carrying amount of the equity component of convertible debt which may be settled in cash upon conversion.

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The price per share of the conversion feature embedded in the debt instrument.

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The ratio applied to the debt for purposes of determining the number of shares of the equity security into which the debt will be converted.

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- Definition

Interest expense related to convertible debt instruments which has been recognized for the period, including the contractual interest coupon and amortization of the debt discount, if any.

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Remaining amortization period for any discount on the liability component of convertible debt which may be settled in cash upon conversion.

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The stated principal amount of the debt instrument at time of issuance, which may vary from the carrying amount because of unamortized premium or discount.

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- Definition

Interest rate stated in the contractual debt agreement.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Date when the debt instrument is scheduled to be fully repaid, which may be presented in a variety of ways (year, month and year, day, month and year, quarter, etc.).

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- Definition

The amount of debt discount that was originally recognized at the issuance of the instrument that has yet to be amortized.

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Fair value as of the balance sheet date of the embedded derivative or group of embedded derivatives classified as a liability.

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Junior subordinated convertible debentures (Details) (USD $)	3 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Mar. 31, 2011	Mar. 31, 2010
Debt Instrument [Line Items]
Principal amount of junior subordinated convertible debentures	$ 1,150,000,000
Interest rate of junior subordinated convertible debentures	2.125%
Due date of junior subordinated convertible debentures	Dec. 15, 2037
Conversion rate, in shares, of junior subordinated convertible debt (in shares per $1,000)	29.2783
Principal amount of junior subordinated convertible debentures used as conversion unit	1,000
Convertible Debt Instrument Initial Conversion Price Per Share	$ 34.16
Debt Instrument, Convertible, Conversion Ratio	34.7365
Debt Instrument, Convertible, Conversion Price	$ 28.79
Carrying value of equity component of the debentures that were bifurcated into a liability and equity component	822,400,000
Estimated fair value of liability component of debentures at issuance date	327,600,000
Debt discount of estimated fair value of liability component of debentures	822,400,000
Amount of unamortized debt discount of debentures	800,100,000		801,900,000
Carrying value of debentures	349,109,000		347,334,000
Remaining period, in years, over which unamortized debt discount will be recognized as non-cash interest expense (in years)	26.5
Amount of non-cash interest expense related to the amortization of debt discount	1,800,000	1,700,000
Recognized amount of interest expense related to debentures	6,100,000	6,100,000
Fair value of derivative on certain embedded features of debentures	390,000	600,000	430,000	700,000
Amount of decrease in interest expense from change in amount of fair value of derivative		$ 100,000