Investments (Details) (USD $) In Millions	Jun. 30, 2011	Dec. 31, 2010
Available-for-sale securities
Amortized cost	$ 8,002	$ 7,643
Gross unrealized gains	549	533
Gross unrealized losses	16	39
Estimated fair value	8,535	8,137
Indemnity
Available-for-sale securities
Amortized cost	535	277
Gross unrealized gains	10	13
Gross unrealized losses	0	2
Estimated fair value	545	288
Indemnity \| Fixed maturities
Available-for-sale securities
Amortized cost	516	257
Gross unrealized gains	9	9
Gross unrealized losses	0	2
Estimated fair value	525	264
Indemnity \| U.S. government & agencies
Available-for-sale securities
Amortized cost	8	25
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Estimated fair value	8	25
Indemnity \| States & political subdivisions
Available-for-sale securities
Amortized cost	214	193
Gross unrealized gains	8	6
Gross unrealized losses	0	2
Estimated fair value	222	197
Indemnity \| Corporate debt securities
Available-for-sale securities
Amortized cost	256	36
Gross unrealized gains	1	2
Gross unrealized losses	0	0
Estimated fair value	257	38
Indemnity \| Other debt securities
Available-for-sale securities
Amortized cost	10
Gross unrealized gains	0
Gross unrealized losses	0
Estimated fair value	10
Indemnity \| Commercial mortgage-backed securities (CMBS)
Available-for-sale securities
Amortized cost	24
Gross unrealized gains	0
Gross unrealized losses	0
Estimated fair value	24
Indemnity \| Collateralized debt obligations (CDO)
Available-for-sale securities
Amortized cost	4	3
Gross unrealized gains	0	1
Gross unrealized losses	0	0
Estimated fair value	4	4
Indemnity \| Nonredeemable preferred stock
Available-for-sale securities
Amortized cost	19	20
Gross unrealized gains	1	4
Gross unrealized losses	0	0
Estimated fair value	20	24
Exchange
Available-for-sale securities
Amortized cost	7,467	7,366
Gross unrealized gains	539	520
Gross unrealized losses	16	37
Estimated fair value	7,990	7,849
Exchange \| Fixed maturities
Available-for-sale securities
Amortized cost	6,929	6,863
Gross unrealized gains	465	446
Gross unrealized losses	14	30
Estimated fair value	7,380	7,279
Exchange \| U.S. government & agencies
Available-for-sale securities
Amortized cost	65	85
Gross unrealized gains	2	2
Gross unrealized losses	0	0
Estimated fair value	67	87
Exchange \| States & political subdivisions
Available-for-sale securities
Amortized cost	1,385	1,437
Gross unrealized gains	56	43
Gross unrealized losses	3	9
Estimated fair value	1,438	1,471
Exchange \| Foreign government securities
Available-for-sale securities
Amortized cost	20	20
Gross unrealized gains	1	1
Gross unrealized losses	0	0
Estimated fair value	21	21
Exchange \| Corporate debt securities
Available-for-sale securities
Amortized cost	5,051	4,900
Gross unrealized gains	383	377
Gross unrealized losses	6	14
Estimated fair value	5,428	5,263
Exchange \| Other debt securities
Available-for-sale securities
Amortized cost	59	54
Gross unrealized gains	2	3
Gross unrealized losses	0	0
Estimated fair value	61	57
Exchange \| Residential mortgage-backed securities (RMBS)
Available-for-sale securities
Amortized cost	212	216
Gross unrealized gains	10	9
Gross unrealized losses	0	1
Estimated fair value	222	224
Exchange \| Commercial mortgage-backed securities (CMBS)
Available-for-sale securities
Amortized cost	68	82
Gross unrealized gains	4	5
Gross unrealized losses	0	1
Estimated fair value	72	86
Exchange \| Collateralized debt obligations (CDO)
Available-for-sale securities
Amortized cost	69	69
Gross unrealized gains	7	6
Gross unrealized losses	5	5
Estimated fair value	71	70
Exchange \| Nonredeemable preferred stock
Available-for-sale securities
Amortized cost	538	503
Gross unrealized gains	74	74
Gross unrealized losses	2	7
Estimated fair value	$ 610	$ 570

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.

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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.

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- 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.

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