Cash Equivalents, and Investments - Maturities of Available for Sale Investments (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013
Schedule of Available For Sale Securities Debt Maturities [Abstract]
Amortized cost due within one year	$ 596.3
Gross Unrealized Gains Due Within One Year	0.4
Gross Unrealized Losses Due Within One Year	0
Estimated fair value due within one year	596.7
Amortized cost due between one and five years	1,013.4
Gross unrealized gains due between one and five years	2.2
Gross Unrealized Losses Due Between One And Five Year	(0.4)
Estimated fair value due between one and five year	1,015.2
Total investments, amortized cost	1,609.7
Gross Unrealized Gains	2.6
Gross Unrealized Losses	(0.4)
Total investments, estimated fair value	$ 1,611.9

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Gross unrealized gains due between une and five years.

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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 fair value maturing in the second fiscal year through the fifth fiscal year following the latest fiscal year.

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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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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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Amount of available-for-sale debt securities at fair value maturing in the next fiscal year following the latest fiscal year.

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