Investments (Details 3) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Net Investment Income:
Investment income, before expense	$ 3,620	$ 4,149	$ 4,221
Investment expense	(161)	(206)	(211)
Net investment income	3,459us-gaap_NetInvestmentIncome	3,943us-gaap_NetInvestmentIncome	4,010us-gaap_NetInvestmentIncome
Fixed income securities
Net Investment Income:
Investment income, before expense	2,447	2,921	3,234
Equity securities
Net Investment Income:
Investment income, before expense	117	149	127
Mortgage loans
Net Investment Income:
Investment income, before expense	265	372	374
Limited partnership interests
Net Investment Income:
Investment income, before expense	614	541	348
Short-term investments
Net Investment Income:
Investment income, before expense	7	5	6
Other
Net Investment Income:
Investment income, before expense	$ 170	$ 161	$ 132

Represents the total of interest and dividend income, including any amortization and accretion (as applicable) of discounts and premiums, earned from (1) loans and leases whether held-for-sale or held-in-portfolio; (2) investment securities; (3) federal funds sold; (4) securities purchased under agreements to resell; (5) investments in banker's acceptances, commercial paper, or certificates of deposit; (6) dividend income; or (7) other investments not otherwise specified herein.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-04.1-5)

-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

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

-Publisher SEC

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+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-04.2)

-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

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

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-Name Accounting Standards Codification

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-Section S99

-Paragraph 2

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Amount, after investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 16

-Article 12

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

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-Name Accounting Standards Codification

-Topic 944

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-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

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