Investments (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Available-for-sale securities
Amortized cost	$ 8,378	$ 7,919
Gross unrealized gains	790	560
Gross unrealized losses	9	50
Total fixed maturities	8,159	7,840
Estimated fair value, equity securities	1,000	589
Estimated fair value	9,159	8,429
Indemnity
Available-for-sale securities
Amortized cost, fixed maturities	437	535
Amortized cost, equity securities	54	24
Amortized cost	491	559
Gross unrealized gains	17	15
Gross unrealized losses	1	1
Total fixed maturities	452	548
Estimated fair value, equity securities	55	25
Estimated fair value	507	573
Indemnity \| Fixed maturities
Available-for-sale securities
Amortized cost, fixed maturities	437	535
Gross unrealized gains	15	14
Gross unrealized losses	0	1
Total fixed maturities	452	548
Indemnity \| States & political subdivisions
Available-for-sale securities
Amortized cost, fixed maturities	172	208
Gross unrealized gains	13	13
Gross unrealized losses	0	0
Total fixed maturities	185	221
Indemnity \| Corporate debt securities
Available-for-sale securities
Amortized cost, fixed maturities	259	303
Gross unrealized gains	2	1
Gross unrealized losses	0	1
Total fixed maturities	261	303
Indemnity \| Commercial mortgage-backed securities (CMBS)
Available-for-sale securities
Amortized cost, fixed maturities	3	13
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Total fixed maturities	3	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
Total fixed maturities	3	4
Indemnity \| Other debt securities
Available-for-sale securities
Amortized cost, fixed maturities		7
Gross unrealized gains		0
Gross unrealized losses		0
Total fixed maturities		7
Indemnity \| Nonredeemable preferred stock
Available-for-sale securities
Amortized cost, equity securities	28	24
Gross unrealized gains	2	1
Gross unrealized losses	1	0
Estimated fair value, equity securities	29	25
Indemnity \| Common stock
Available-for-sale securities
Amortized cost, equity securities	26
Gross unrealized gains	0
Gross unrealized losses	0
Estimated fair value, equity securities	26
Exchange
Available-for-sale securities
Amortized cost, fixed maturities	7,016	6,829
Amortized cost, equity securities	871	531
Amortized cost	7,887	7,360
Gross unrealized gains	773	545
Gross unrealized losses	8	49
Total fixed maturities	7,707	7,292
Estimated fair value, equity securities	945	564
Estimated fair value	8,652	7,856
Exchange \| Fixed maturities
Available-for-sale securities
Amortized cost, fixed maturities	7,016	6,829
Gross unrealized gains	696	500
Gross unrealized losses	5	37
Total fixed maturities	7,707	7,292
Exchange \| U.S. government & agencies
Available-for-sale securities
Amortized cost, fixed maturities	190	16
Gross unrealized gains	2	1
Gross unrealized losses	1	0
Total fixed maturities	191	17
Exchange \| States & political subdivisions
Available-for-sale securities
Amortized cost, fixed maturities	1,218	1,289
Gross unrealized gains	103	91
Gross unrealized losses	0	1
Total fixed maturities	1,321	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
Total fixed maturities	16	15
Exchange \| Corporate debt securities
Available-for-sale securities
Amortized cost, fixed maturities	5,211	5,144
Gross unrealized gains	569	386
Gross unrealized losses	3	31
Total fixed maturities	5,777	5,499
Exchange \| Residential mortgage-backed securities (RMBS)
Available-for-sale securities
Amortized cost, fixed maturities	226	178
Gross unrealized gains	6	11
Gross unrealized losses	1	0
Total fixed maturities	231	189
Exchange \| Commercial mortgage-backed securities (CMBS)
Available-for-sale securities
Amortized cost, fixed maturities	62	62
Gross unrealized gains	5	4
Gross unrealized losses	0	0
Total fixed maturities	67	66
Exchange \| Collateralized debt obligations (CDO)
Available-for-sale securities
Amortized cost, fixed maturities	43	66
Gross unrealized gains	6	4
Gross unrealized losses	0	5
Total fixed maturities	49	65
Exchange \| Other debt securities
Available-for-sale securities
Amortized cost, fixed maturities	51	59
Gross unrealized gains	4	3
Gross unrealized losses	0	0
Total fixed maturities	55	62
Exchange \| Nonredeemable preferred stock
Available-for-sale securities
Amortized cost, equity securities	555	531
Gross unrealized gains	77	45
Gross unrealized losses	1	12
Estimated fair value, equity securities	631	564
Exchange \| Common stock
Available-for-sale securities
Amortized cost, equity securities	316
Gross unrealized gains	0
Gross unrealized losses	2
Estimated fair value, equity securities	$ 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

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+ Details

- Definition

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

+ References

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+ 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