Investments (Details 4) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Investment income from portfolios
Investment income, net of expenses	$ 433	$ 433	$ 433
Indemnity
Investment income from portfolios
Total investment income	17	38	42
Less: Investment expenses	1	1	0
Investment income, net of expenses	16	37	42
Increase (decrease) in net investment income	(21)
Indemnity \| Fixed maturities
Investment income from portfolios
Total investment income	14	33	36
Indemnity \| Equity securities
Investment income from portfolios
Total investment income	2	4	5
Indemnity \| Cash equivalents and other
Investment income from portfolios
Total investment income	1	1	1
Exchange
Investment income from portfolios
Total investment income	450	424	415
Less: Investment expenses	33	28	24
Investment income, net of expenses	417	396	391
Increase (decrease) in net investment income	21
Exchange \| Fixed maturities
Investment income from portfolios
Total investment income	364	350	343
Exchange \| Equity securities
Investment income from portfolios
Total investment income	86	72	68
Exchange \| Cash equivalents and other
Investment income from portfolios
Total investment income	$ 0	$ 2	$ 4

The increase (decrease) in income earned from investments in securities and property, equipment and other capital assets.

No definition available.

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- Definition

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.

+ References

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

-Publisher AICPA

-Name Audit and Accounting Guide (AAG)

-Number AAG-BRD

-Chapter 4

-Paragraph 9, 51, 54

-IssueDate 2006-05-01

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 9

-Section 04

-Paragraph 1, 2 , 3, 4, 5

Reference 3: 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

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- Definition

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

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.9)

-URI http://asc.fasb.org/extlink&oid=6880815&loc=d3e20235-122688

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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

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph 2

-Article 7

Reference 3: 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

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