Marketable Debt Securities Continuous Unrealized Losses (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months Fair Value	$ 163.2	$ 388.3
Less than 12 Months Unrealized Losses	0.1	0.9
12 Months or Greater Fair value	26.8	28.4
12 Months or Greater Unrealized losses	$ 0.2	$ 0.1

Amount of accumulated pre-tax unrealized loss on securities classified as available-for-sale that have been in a loss position for twelve months or longer impacting investments.

No definition available.

+ Details

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- Definition

Amount of accumulated pre-tax unrealized loss on investments in available-for-sale securities that have been in a loss position for less than twelve months impacting investments.

+ References

No definition available.

+ Details

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- Details

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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

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 7

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27337-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 6

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563

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- Definition

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
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Period Type:	instant