Financial Instruments (Contractual Maturities Of Available-For-Sale Investments In Debt Securities) (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Mar. 31, 2012
Investments Debt And Equity Securities [Abstract]
Due in one year or less, Cost	$ 206.2	$ 136.0
Due between one and two years, Cost	30.7	6.1
Due after ten years, Cost	21.6	29.3
Maturities of available-for-sale investments in debt securities at Cost	258.5	171.4
Due in one year or less, Fair Value	206.2	136.0
Due between one and two years, Fair Value	30.7	6.1
Due after ten years, Fair Value	19.9	26.9
Maturities of available-for-sale investments in debt securities at Fair Value	$ 256.8	$ 169.0

Amount of available-for-sale debt securities at cost, net of adjustments, maturing in the second fiscal year through the fifth fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings (less any cumulative-effect adjustments, as defined) and fair value hedge accounting adjustments.

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Amount of available-for-sale debt securities at cost, net of adjustments, maturing after the tenth fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings (less any cumulative-effect adjustments, as defined) and fair value hedge accounting adjustments.

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- Definition

Amount of available-for-sale debt securities at cost, net of adjustments, which include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings (less any cumulative-effect adjustments, as defined) and fair value hedge accounting adjustments.

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- Definition

Amount of available-for-sale debt securities at cost, net of adjustments, maturing in the next fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings (less any cumulative-effect adjustments, as defined) and fair value hedge accounting adjustments.

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- Definition

Amount of debt securities categorized neither as held-to-maturity nor trading.

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