Cash Equivalent and Investments (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
Mar. 31, 2015	Dec. 31, 2014
Schedule Of Available For Sale Securities LineItems
Fair Value	$ 47.3us-gaap_AvailableForSaleSecurities	$ 48.0us-gaap_AvailableForSaleSecurities
money market
Schedule Of Available For Sale Securities LineItems
Cost		149.7
Gross Unrealized Gain	0	0
Fair Value	100.5	149.7
Certificates Of Deposit Member
Schedule Of Available For Sale Securities LineItems
Cost	1,217.2	842.5
Gross Unrealized Gain	0	0
Fair Value	1,217.2	842.5
fixed maturity and mutual funds [Member]
Schedule Of Available For Sale Securities LineItems
Cost	45.3	47.1
Gross Unrealized Gain	2.0	0.9
Fair Value	47.3	48.0
CashAndCashEquivalentsMember \| money market
Schedule Of Available For Sale Securities LineItems
Fair Value	100.5	149.7
CashAndCashEquivalentsMember \| Certificates Of Deposit Member
Schedule Of Available For Sale Securities LineItems
Fair Value	727.4	380.1
CashAndCashEquivalentsMember \| fixed maturity and mutual funds [Member]
Schedule Of Available For Sale Securities LineItems
Fair Value	0	0
Short Term Investments Member \| money market
Schedule Of Available For Sale Securities LineItems
Fair Value	0	0
Short Term Investments Member \| Certificates Of Deposit Member
Schedule Of Available For Sale Securities LineItems
Fair Value	485.5	458.1
Short Term Investments Member \| fixed maturity and mutual funds [Member]
Schedule Of Available For Sale Securities LineItems
Fair Value	0	0
Other Assets [Member] \| money market
Schedule Of Available For Sale Securities LineItems
Fair Value	0	0
Other Assets [Member] \| Certificates Of Deposit Member
Schedule Of Available For Sale Securities LineItems
Fair Value	4.3	4.3
Other Assets [Member] \| fixed maturity and mutual funds [Member]
Schedule Of Available For Sale Securities LineItems
Fair Value	$ 47.3	$ 48.0

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=28360136&loc=d3e22054-111558

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 5

-Subparagraph (aa)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 45

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- Definition

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.2)

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- Definition

Amount of unrealized gain before deducting unrealized loss on investments in debt and equity securities classified as available-for-sale securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563

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