Investments - Repurchase Agreement, Securities Lending, VIEs (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
Sep. 30, 2013	Dec. 31, 2012
Available-for-sale Securities Including Securities Pledged [Line Items]
Required collateral percentage of market value of loaned securities	102.00%
Percentage lending agent may retain, percentage of collateral	5.00%
Fair value of loaned securities	$ 159.9	$ 180.2
Securities received as collateral	167.1	186.1
Payables under securities loan agreement, including collateral held	307.8	353.2
Collateralized loan obligations \| Not a primary beneficiary of the VIE
Variable Interest Entity, Not Primary Beneficiary, Disclosures [Abstract]
Carrying value of VIE	1.1	1.3
Securities pledged as collateral
Available-for-sale Securities Including Securities Pledged [Line Items]
Fair value of loaned securities	159.9	180.2
Payables under securities loan agreement, including collateral held
Available-for-sale Securities Including Securities Pledged [Line Items]
Payables under securities loan agreement, including collateral held	$ 167.1	$ 186.1

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Securities Lending, Percentage Lending Agent May Retain, Percentage Of Collateral

+ References

No definition available.

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- Definition

Securities Lending, Required Collateral Percentage Of Market Value Of Loaned Securities

+ References

No definition available.

+ Details

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- Definition

The fair value of collateral received by the entity associated with securities borrowed that must be returned if the counterparty fulfills its obligations. It appears on the balance sheet as a liability and has a corresponding asset that appears on the balance sheet called Securities Received as Collateral.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.15)

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Collateral

-URI http://asc.fasb.org/extlink&oid=6507830

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- Definition

Fair value of the securities pledged as collateral against securities loaned.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 20

-Section 55

-Paragraph 12

-URI http://asc.fasb.org/extlink&oid=28370219&loc=SL20226013-175313

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- Definition

The carrying value as of the balance sheet date of the assets received as collateral against securities loaned to other broker-dealers. Borrowers of securities generally are required to provide collateral to the lenders of securities, commonly cash but sometimes other securities or standby letters of credit, with a value slightly higher than that of the securities borrowed. In instances where the entity is permitted to sell or re-pledge these securities, the entity reports the fair value of the collateral received and the related obligation to return the collateral as a liability.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 30

-Section 50

-Paragraph 1A

-Subparagraph (b)(1)

-URI http://asc.fasb.org/extlink&oid=7523297&loc=SL6224234-111729

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 10

-Section 05

-Paragraph 17

-URI http://asc.fasb.org/extlink&oid=7517284&loc=d3e93645-111703

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- Definition

Carrying amount of the assets in the reporting entity's statement of financial position that relate to the reporting entity's variable interest in the Variable Interest Entity (VIE), where the reporting entity is not the VIE's primary beneficiary.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 810

-SubTopic 10

-Section 50

-Paragraph 4

-Subparagraph a

-URI http://asc.fasb.org/extlink&oid=28200181&loc=d3e5728-111685

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