Investments (Schedule Of Investment Income And Expenses) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Interest and dividends on fixed maturities	$ 121.4	$ 130.7	$ 133.6
Dividends on equity securities	9.6	8.7	7.9
Interest on short-term and other investments	4.7	2.6	5.7
Other	(0.5)	(0.1)	7.7
Investment income	135.2	141.9	154.9
Investment expenses	(9.4)	(8.3)	(9.4)
Net investment income	$ 125.8	$ 133.6	$ 145.5

Other investment income

No definition available.

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- Definition

Investment income associated with the company's insurance services.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 225

-Section S99

-Paragraph 1

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- Definition

Income derived from investments in equity securities representing a distribution of earnings to shareholders by the investee companies.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 14

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 7

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-Publisher FASB

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-Topic 225

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-Subparagraph (SX 210.5-03.7(a))

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- Definition

Income derived from investments in debt securities and on cash and cash equivalents the earnings of which reflect the time value of money or transactions in which the payments are for the use or forbearance of money.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 14

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

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- Definition

Income derived from investments in debt and equity securities and on cash and cash equivalents. Interest income represents earnings which reflect the time value of money or transactions in which the payments are for the use or forbearance of money. Dividend income represents a distribution of earnings to shareholders by investee companies.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 14

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

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-Subparagraph (SX 210.5-03.7(a),(b))

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- Definition

Total expenses related to the generation of investment income in debt and equity securities.

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-Name Accounting Standards Codification

-Topic 225

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- Definition

The income earned from investments in securities and property, equipment and other capital assets. It includes rent from property and equipment, dividends from shares in corporations, and interest from bonds, loans, mortgages, derivatives, commercial paper, bank accounts, certificates of deposits, treasuries, and other financial securities. It does not include realized gains and losses on investments.

+ References

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 16

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