Fair Value (Reconciliation Of The Beginning And Ending Balances Of Assets Measured At Fair Value On A Recurring Basis Using Level III Inputs) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2013	Mar. 31, 2012
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	$ 155.5	$ 284.8
Recognized in net income	0.9	14.9
Recognized in accumulated other comprehensive income	(1.3)	(20.2)
Purchases	10.0	18.8
Sales	(2.5)	(1.9)
Issuances	0	0
Settlements	(10.9)	(52.2)
Transfers into Level III	13.1	1.4
Transfers out of Level III	(2.9)	(105.7)
Ending balance	161.9	139.9
Change in unrealized losses included in net income related to assets still held	(1.4)	(0.4)
Corporate Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	121.1	195.1
Recognized in net income	0.3	15.2
Recognized in accumulated other comprehensive income	(0.6)	(16.9)
Purchases	9.6	18.8
Sales	0	(1.9)
Issuances	0	0
Settlements	(9.1)	(51.7)
Transfers into Level III	0	0
Transfers out of Level III	0	(49.4)
Ending balance	121.3	109.2
Change in unrealized losses included in net income related to assets still held	0	0
Residential Mortgage-Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	4.3	0
Recognized in net income	0	0
Recognized in accumulated other comprehensive income	0	0
Purchases	0	0
Sales	0	0
Issuances	0	0
Settlements	(1.6)	0
Transfers into Level III	13.1	1.4
Transfers out of Level III	(2.9)	0
Ending balance	12.9	1.4
Change in unrealized losses included in net income related to assets still held	0	0
Commercial Mortgage-Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	0	6.3
Recognized in net income	0	0
Recognized in accumulated other comprehensive income	0	0
Purchases	0	0
Sales	0	0
Issuances	0	0
Settlements	0	0
Transfers into Level III	0	0
Transfers out of Level III	0	(6.3)
Ending balance	0	0
Change in unrealized losses included in net income related to assets still held	0	0
Other Debt Obligations [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	3.9	59.0
Recognized in net income	0	0.1
Recognized in accumulated other comprehensive income	0.2	0.1
Purchases	0	0
Sales	0	0
Issuances	0	0
Settlements	(0.2)	(0.5)
Transfers into Level III	0	0
Transfers out of Level III	0	(50.0)
Ending balance	3.9	8.7
Change in unrealized losses included in net income related to assets still held	0	0
Equity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	26.2	24.4
Recognized in net income	0.6	(0.4)
Recognized in accumulated other comprehensive income	(0.9)	(3.4)
Purchases	0.4	0
Sales	(2.5)	0
Issuances	0	0
Settlements	0	0
Transfers into Level III	0	0
Transfers out of Level III	0	0
Ending balance	23.8	20.6
Change in unrealized losses included in net income related to assets still held	$ (1.4)	$ (0.4)

This item represents the amount of the total change in unrealized (holding) gains or losses for the period which are included in the statement of income (or changes in net assets) in investment income. Such unrealized (holding) gains or losses relate to those assets still held at the reporting date for which fair value is measured on a recurring basis using significant unobservable inputs (Level 3).

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=7578670&loc=d3e19207-110258

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 157

-Paragraph 32

-Subparagraph d

-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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- Definition

Amount of gain (loss) recognized in earnings, arising from assets measured at fair value on a recurring basis using unobservable inputs (level 3).

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- Definition

Amount of gain (loss) recognized in other comprehensive income, arising from assets measured at fair value on a recurring basis using unobservable inputs (level 3).

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- Definition

Issues that have taken place during the period in relation to assets measured at fair value and categorized within Level 3 of the fair value hierarchy.

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- Definition

Purchases that have taken place during the period in relation to assets measured at fair value and categorized within Level 3 of the fair value hierarchy.

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- Definition

Sales that have taken place during the period in relation to assets measured at fair value and categorized within Level 3 of the fair value hierarchy.

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- Definition

Settlements that have taken place during the period in relation to assets measured at fair value and categorized within Level 3 of the fair value hierarchy.

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- Definition

Transfers into assets measured at fair value and categorized within Level 3 of the fair value hierarchy that have taken place during the period.

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- Definition

Transfers out of assets measured at fair value and categorized within Level 3 of the fair value hierarchy that have taken place during the period.

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- Definition

This element represents an asset measured at fair value using significant unobservable inputs (Level 3) which is required for reconciliation purposes of beginning and ending balances.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=7578670&loc=d3e19207-110258

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 157

-Paragraph 32

-Subparagraph c

-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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