Investments (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Available-for-sale securities
Amortized cost	$ 8,751	$ 8,378
Gross unrealized gains	528	790
Gross unrealized losses	99	9
Estimated fair value, fixed maturities	8,163	8,159
Estimated fair value, equity securities	1,017	1,000
Estimated fair value	9,180	9,159
Indemnity
Available-for-sale securities
Amortized cost, fixed maturities	430	437
Amortized cost, equity securities	47	54
Amortized cost	477	491
Gross unrealized gains	11	17
Gross unrealized losses	2	1
Estimated fair value, fixed maturities	438	452
Estimated fair value, equity securities	48	55
Estimated fair value	486	507
Indemnity \| Fixed maturities
Available-for-sale securities
Amortized cost, fixed maturities	430	437
Gross unrealized gains	9	15
Gross unrealized losses	1	0
Estimated fair value, fixed maturities	438	452
Indemnity \| States & political subdivisions
Available-for-sale securities
Amortized cost, fixed maturities	172	172
Gross unrealized gains	7	13
Gross unrealized losses	0	0
Estimated fair value, fixed maturities	179	185
Indemnity \| Corporate debt securities
Available-for-sale securities
Amortized cost, fixed maturities	257	259
Gross unrealized gains	2	2
Gross unrealized losses	1	0
Estimated fair value, fixed maturities	258	261
Indemnity \| Commercial mortgage-backed securities
Available-for-sale securities
Amortized cost, fixed maturities		3
Gross unrealized gains		0
Gross unrealized losses		0
Estimated fair value, fixed maturities		3
Indemnity \| Collateralized debt obligations
Available-for-sale securities
Amortized cost, fixed maturities	1	3
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Estimated fair value, fixed maturities	1	3
Indemnity \| Nonredeemable preferred stock
Available-for-sale securities
Amortized cost, equity securities	21	28
Gross unrealized gains	2	2
Gross unrealized losses	0	1
Estimated fair value, equity securities	23	29
Indemnity \| Common stock
Available-for-sale securities
Amortized cost, equity securities	26	26
Gross unrealized gains	0	0
Gross unrealized losses	1	0
Estimated fair value, equity securities	25	26
Exchange
Available-for-sale securities
Amortized cost, fixed maturities	7,359	7,016
Amortized cost, equity securities	915	871
Amortized cost	8,274	7,887
Gross unrealized gains	517	773
Gross unrealized losses	97	8
Estimated fair value, fixed maturities	7,725	7,707
Estimated fair value, equity securities	969	945
Estimated fair value	8,694	8,652
Exchange \| Fixed maturities
Available-for-sale securities
Amortized cost, fixed maturities	7,359	7,016
Gross unrealized gains	443	696
Gross unrealized losses	77	5
Estimated fair value, fixed maturities	7,725	7,707
Exchange \| U.S. government & agencies
Available-for-sale securities
Amortized cost, fixed maturities	188	190
Gross unrealized gains	1	2
Gross unrealized losses	5	1
Estimated fair value, fixed maturities	184	191
Exchange \| States & political subdivisions
Available-for-sale securities
Amortized cost, fixed maturities	1,226	1,218
Gross unrealized gains	61	103
Gross unrealized losses	13	0
Estimated fair value, fixed maturities	1,274	1,321
Exchange \| Foreign government securities
Available-for-sale securities
Amortized cost, fixed maturities	23	15
Gross unrealized gains	1	1
Gross unrealized losses	1	0
Estimated fair value, fixed maturities	23	16
Exchange \| Corporate debt securities
Available-for-sale securities
Amortized cost, fixed maturities	5,570	5,211
Gross unrealized gains	365	569
Gross unrealized losses	53	3
Estimated fair value, fixed maturities	5,882	5,777
Exchange \| Residential mortgage-backed securities
Available-for-sale securities
Amortized cost, fixed maturities	222	226
Gross unrealized gains	3	6
Gross unrealized losses	4	1
Estimated fair value, fixed maturities	221	231
Exchange \| Commercial mortgage-backed securities
Available-for-sale securities
Amortized cost, fixed maturities	48	62
Gross unrealized gains	2	5
Gross unrealized losses	1	0
Estimated fair value, fixed maturities	49	67
Exchange \| Collateralized debt obligations
Available-for-sale securities
Amortized cost, fixed maturities	16	43
Gross unrealized gains	7	6
Gross unrealized losses	0	0
Estimated fair value, fixed maturities	23	49
Exchange \| Other debt securities
Available-for-sale securities
Amortized cost, fixed maturities	66	51
Gross unrealized gains	3	4
Gross unrealized losses	0	0
Estimated fair value, fixed maturities	69	55
Exchange \| Nonredeemable preferred stock
Available-for-sale securities
Amortized cost, equity securities	577	555
Gross unrealized gains	74	77
Gross unrealized losses	4	1
Estimated fair value, equity securities	647	631
Exchange \| Common stock
Available-for-sale securities
Amortized cost, equity securities	338	316
Gross unrealized gains	0	0
Gross unrealized losses	16	2
Estimated fair value, equity securities	$ 322	$ 314

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 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 2: 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 3: 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 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 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 6: 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 7: 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.

Reference 8: 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 9: 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 10: 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

+ 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 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 2: 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 3: 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 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 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 6: 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 7: 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.

Reference 8: 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 9: 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 10: 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

+ 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