Investments (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Investments in short and long-term classified as available-for-sale securities
Available-for-sale Securities, Amortized Cost	$ 751.8	$ 672.7
Available-for-sale Securities, Gross Unrealized Gains	0.4	0.3
Available-for-sale Securities, Gross Unrealized Losses	(0.2)	(0.3)
Available-for-sale Securities, Fair Value	752.0	672.7
Fair values and gross unrealized losses for all available-for-sale securities in an unrealized loss position deemed to be temporary
Available-for-sale Securities, Unrealized Losses, Fair Value	304.1	164.5
Available-for-sale Securities, Unrealized Losses	(0.2)	(0.3)
Corporate debt securities [Member]
Investments in short and long-term classified as available-for-sale securities
Available-for-sale Securities, Amortized Cost	331.1	324.8
Available-for-sale Securities, Gross Unrealized Gains	0.4	0.2
Available-for-sale Securities, Gross Unrealized Losses	(0.1)	(0.3)
Available-for-sale Securities, Fair Value	331.4	324.7
Fair values and gross unrealized losses for all available-for-sale securities in an unrealized loss position deemed to be temporary
Available-for-sale Securities, Unrealized Losses, Fair Value	131.1	164.5
Available-for-sale Securities, Unrealized Losses	(0.1)	(0.3)
U.S. Government Agencies and Debt Securities [Member]
Investments in short and long-term classified as available-for-sale securities
Available-for-sale Securities, Amortized Cost	200.5	177.1
Available-for-sale Securities, Gross Unrealized Gains		0.1
Available-for-sale Securities, Gross Unrealized Losses	(0.1)
Available-for-sale Securities, Fair Value	200.4	177.2
Fair values and gross unrealized losses for all available-for-sale securities in an unrealized loss position deemed to be temporary
Available-for-sale Securities, Unrealized Losses, Fair Value	173.0
Available-for-sale Securities, Unrealized Losses	(0.1)
Municipal Bonds [Member]
Investments in short and long-term classified as available-for-sale securities
Available-for-sale Securities, Amortized Cost		1.0
Available-for-sale Securities, Fair Value		1.0
Foreign government debt securities [Member]
Investments in short and long-term classified as available-for-sale securities
Available-for-sale Securities, Amortized Cost	2.8	6.8
Available-for-sale Securities, Fair Value	2.8	6.8
Commercial Paper [Member]
Investments in short and long-term classified as available-for-sale securities
Available-for-sale Securities, Amortized Cost	127.3	74.5
Available-for-sale Securities, Fair Value	127.3	74.5
Certificates of deposit [Member]
Investments in short and long-term classified as available-for-sale securities
Available-for-sale Securities, Amortized Cost	90.1	88.5
Available-for-sale Securities, Fair Value	$ 90.1	$ 88.5

This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for less than twelve months.

+ References+ Details

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 Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

+ References+ Details

- 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+ Details