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Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27290-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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- Definition

Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale in a continuous loss position.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27337-111563

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This item represents the aggregate fair value of investments in debt and equity securities in an unrealized loss position which are categorized neither as held-to-maturity nor trading securities.

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Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for less than twelve months.

+ References

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- Definition

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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-Section 50
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This item represents the gross loss realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

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The amount of other than temporary impairment losses on investments in debt and equity securities categorized as Available-for-sale which have been recognized in earnings during the period. Such impairment losses consist of other than temporary impairments (OTTI) on equity securities, credit losses on investments in debt securities, and when the entity intends to sell an impaired debt security or it is more likely than not that the entity will be required to sell the impaired debt security before recovery of its amortized cost basis.

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Short-term Investments (Available-For-Sale Securities In A Continuous Unrealized Loss Position) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Jun. 30, 2016	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Schedule of Short-term Investments [Table] [Line Items]
Fair Value available-for-sale securities Less than 12 Months	$ 801.4			$ 801.4		$ 1,318.2
Unrealized losses, available-for-sale securities, Less than 12 Months	(1.1)			(1.1)		(4.2)
Fair value available-for-sale securities 12 Months or More	2.1			2.1		35.6
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities	0.0			0.0		(3.2)
Total Fair Value available-for-sale securities	803.5			803.5		1,353.8
Unrealized losses, available-for-sale securities, Total	(1.1)			(1.1)		(7.4)
Realized loss from sale of investment	3.2	$ 0.1		3.6	$ 0.2
U.S. Treasury And Agency Debt Securities [Member]
Schedule of Short-term Investments [Table] [Line Items]
Fair Value available-for-sale securities Less than 12 Months	210.6			210.6		475.7
Unrealized losses, available-for-sale securities, Less than 12 Months	(0.3)			(0.3)		(1.8)
Fair value available-for-sale securities 12 Months or More	0.0			0.0		0.0
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities	0.0			0.0		0.0
Total Fair Value available-for-sale securities	210.6			210.6		475.7
Unrealized losses, available-for-sale securities, Total	(0.3)			(0.3)		(1.8)
Corporate And Other Debt Securities [Member]
Schedule of Short-term Investments [Table] [Line Items]
Fair Value available-for-sale securities Less than 12 Months	116.9			116.9		315.1
Unrealized losses, available-for-sale securities, Less than 12 Months	(0.2)			(0.2)		(1.5)
Fair value available-for-sale securities 12 Months or More	0.9			0.9		3.1
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities	0.0			0.0		0.0
Total Fair Value available-for-sale securities	117.8			117.8		318.2
Unrealized losses, available-for-sale securities, Total	(0.2)			(0.2)		(1.5)
Certificates of Deposit and Commercial Paper [Member]
Schedule of Short-term Investments [Table] [Line Items]
Fair Value available-for-sale securities Less than 12 Months	368.1			368.1		271.5
Unrealized losses, available-for-sale securities, Less than 12 Months	(0.4)			(0.4)		(0.1)
Fair value available-for-sale securities 12 Months or More	0.0			0.0		0.0
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities	0.0			0.0		0.0
Total Fair Value available-for-sale securities	368.1			368.1		271.5
Unrealized losses, available-for-sale securities, Total	(0.4)			(0.4)		(0.1)
Asset-Backed Securities [Member]
Schedule of Short-term Investments [Table] [Line Items]
Fair Value available-for-sale securities Less than 12 Months	62.8			62.8		199.4
Unrealized losses, available-for-sale securities, Less than 12 Months	(0.1)			(0.1)		(0.7)
Fair value available-for-sale securities 12 Months or More	0.6			0.6		11.4
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities	0.0			0.0		(0.1)
Total Fair Value available-for-sale securities	63.4			63.4		210.8
Unrealized losses, available-for-sale securities, Total	(0.1)			(0.1)		(0.8)
Municipal Debt Securities [Member]
Schedule of Short-term Investments [Table] [Line Items]
Fair Value available-for-sale securities Less than 12 Months	43.0			43.0		56.5
Unrealized losses, available-for-sale securities, Less than 12 Months	(0.1)			(0.1)		(0.1)
Fair value available-for-sale securities 12 Months or More	0.6			0.6		0.0
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities	0.0			0.0		0.0
Total Fair Value available-for-sale securities	43.6			43.6		56.5
Unrealized losses, available-for-sale securities, Total	(0.1)			$ (0.1)		(0.1)
Mutual Funds [Member]
Schedule of Short-term Investments [Table] [Line Items]
Fair Value available-for-sale securities Less than 12 Months						0.0
Unrealized losses, available-for-sale securities, Less than 12 Months						0.0
Fair value available-for-sale securities 12 Months or More			$ 21.7			21.1
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities						(3.1)
Total Fair Value available-for-sale securities						21.1
Unrealized losses, available-for-sale securities, Total						$ (3.1)
Impairment loss recognized in earnings			$ 3.0
Realized loss from sale of investment	$ 3.1