Investments (Concentrations of Credit Risk - Narrative) (Details) (USD $) In Billions, unless otherwise specified	9 Months Ended
Sep. 30, 2013	Sep. 30, 2013 Foreign government debt securities [Member] Japan [Member]	Dec. 31, 2012 Foreign government debt securities [Member] Japan [Member]	Sep. 30, 2013 Fixed maturity and equity securities [Member] Japan [Member]	Dec. 31, 2012 Fixed maturity and equity securities [Member] Japan [Member]
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Securities holdings exposure in single issuer greater than stated percentage of Company's equity	10.00%
Government and agency fixed maturity securities		$ 21.2	$ 22.4	$ 26.4	$ 28.7

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 21

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=28364263&loc=d3e13537-108611

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 275

-SubTopic 10

-Section 50

-Paragraph 20

-URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6404-108592

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 20

-URI http://asc.fasb.org/extlink&oid=28364263&loc=d3e13531-108611

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 275

-SubTopic 10

-Section 50

-Paragraph 18

-URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6351-108592

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