Investments (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Available-for-sale securities
Amortized cost	$ 8,010	$ 7,919
Gross unrealized gains	820	560
Gross unrealized losses	7	50
Estimated fair value, fixed maturities	8,170	7,840
Estimated fair value, equity securities	653	589
Estimated fair value	8,823	8,429
Indemnity
Available-for-sale securities
Amortized cost, fixed maturities	531	535
Amortized cost, equity securities	27	24
Amortized cost	558	559
Gross unrealized gains	18	15
Gross unrealized losses	0	1
Estimated fair value, fixed maturities	547	548
Estimated fair value, equity securities	29	25
Estimated fair value	576	573
Indemnity \| Fixed maturities
Available-for-sale securities
Amortized cost, fixed maturities	531	535
Gross unrealized gains	16	14
Gross unrealized losses	0	1
Estimated fair value, fixed maturities	547	548
Indemnity \| States & political subdivisions
Available-for-sale securities
Amortized cost, fixed maturities	181	208
Gross unrealized gains	14	13
Gross unrealized losses	0	0
Estimated fair value, fixed maturities	195	221
Indemnity \| Corporate debt securities
Available-for-sale securities
Amortized cost, fixed maturities	333	303
Gross unrealized gains	2	1
Gross unrealized losses	0	1
Estimated fair value, fixed maturities	335	303
Indemnity \| Commercial mortgage-backed securities (CMBS)
Available-for-sale securities
Amortized cost, fixed maturities	6	13
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Estimated fair value, fixed maturities	6	13
Indemnity \| Collateralized debt obligations (CDO)
Available-for-sale securities
Amortized cost, fixed maturities	3	4
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Estimated fair value, fixed maturities	3	4
Indemnity \| Other debt securities
Available-for-sale securities
Amortized cost, fixed maturities	8	7
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Estimated fair value, fixed maturities	8	7
Indemnity \| Nonredeemable preferred stock
Available-for-sale securities
Amortized cost, equity securities	27	24
Gross unrealized gains	2	1
Gross unrealized losses	0	0
Estimated fair value, equity securities	29	25
Exchange
Available-for-sale securities
Amortized cost, fixed maturities	6,909	6,829
Amortized cost, equity securities	543	531
Amortized cost	7,452	7,360
Gross unrealized gains	802	545
Gross unrealized losses	7	49
Estimated fair value, fixed maturities	7,623	7,292
Estimated fair value, equity securities	624	564
Estimated fair value	8,247	7,856
Exchange \| Fixed maturities
Available-for-sale securities
Amortized cost, fixed maturities	6,909	6,829
Gross unrealized gains	719	500
Gross unrealized losses	5	37
Estimated fair value, fixed maturities	7,623	7,292
Exchange \| U.S. government & agencies
Available-for-sale securities
Amortized cost, fixed maturities	16	16
Gross unrealized gains	1	1
Gross unrealized losses	0	0
Estimated fair value, fixed maturities	17	17
Exchange \| States & political subdivisions
Available-for-sale securities
Amortized cost, fixed maturities	1,238	1,289
Gross unrealized gains	111	91
Gross unrealized losses	1	1
Estimated fair value, fixed maturities	1,348	1,379
Exchange \| Foreign government securities
Available-for-sale securities
Amortized cost, fixed maturities	15	15
Gross unrealized gains	1	0
Gross unrealized losses	0	0
Estimated fair value, fixed maturities	16	15
Exchange \| Corporate debt securities
Available-for-sale securities
Amortized cost, fixed maturities	5,306	5,144
Gross unrealized gains	584	386
Gross unrealized losses	4	31
Estimated fair value, fixed maturities	5,886	5,499
Exchange \| Residential mortgage-backed securities (RMBS)
Available-for-sale securities
Amortized cost, fixed maturities	166	178
Gross unrealized gains	8	11
Gross unrealized losses	0	0
Estimated fair value, fixed maturities	174	189
Exchange \| Commercial mortgage-backed securities (CMBS)
Available-for-sale securities
Amortized cost, fixed maturities	67	62
Gross unrealized gains	5	4
Gross unrealized losses	0	0
Estimated fair value, fixed maturities	72	66
Exchange \| Collateralized debt obligations (CDO)
Available-for-sale securities
Amortized cost, fixed maturities	57	66
Gross unrealized gains	5	4
Gross unrealized losses	0	5
Estimated fair value, fixed maturities	62	65
Exchange \| Other debt securities
Available-for-sale securities
Amortized cost, fixed maturities	44	59
Gross unrealized gains	4	3
Gross unrealized losses	0	0
Estimated fair value, fixed maturities	48	62
Exchange \| Nonredeemable preferred stock
Available-for-sale securities
Amortized cost, equity securities	543	531
Gross unrealized gains	83	45
Gross unrealized losses	2	12
Estimated fair value, equity securities	$ 624	$ 564

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References+ Details

Amount of debt securities categorized neither as held-to-maturity nor trading.

+ References

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

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS115-1/124-1

-Paragraph 15C

-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 FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 12

-Subparagraph b

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 137

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 16

-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 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 320

-Section 50

-Paragraph 2

-Subparagraph (b)-(g)

-URI http://asc.fasb.org/extlink&oid=6957658&loc=d3e62557-112803

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=7534914&loc=d3e22054-111558

Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562

Reference 8: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 22

-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 9: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 13

-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 10: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS115-1/124-1

-Paragraph 15D

-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.

+ Details

- Definition

Amount of equity securities categorized neither as held-to-maturity nor as trading.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 3

-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.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 12

-Subparagraph b

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

-Publisher FASB

-Name Emerging Issues Task Force (EITF)

-Number 86-40

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 16

-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 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 320

-Section 50

-Paragraph 2

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6957658&loc=d3e62557-112803

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=7534914&loc=d3e22054-111558

Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562

Reference 8: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 22

-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 9: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 13

-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 10: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 19

-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.

+ Details

- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

+ References+ Details

- Definition

This item represents the gross unrealized gains for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

+ References+ Details