Investments (Details 5) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Realized gains (losses) on investments
Net realized investment gains (losses)	$ 191	$ 169	$ 501	$ 358
Other-than-temporary impairments on investments
Net impairment losses recognized in earnings	9	0	10	0
Indemnity
Realized gains (losses) on investments
Net realized investment gains (losses)	1	2	1	4
Other-than-temporary impairments on investments
Other -than-temporary impairments on investments	0	0	0	0
Portion recognized in other comprehensive income	0	0	0	0
Net impairment losses recognized in earnings	0	0	0	0
Indemnity \| Fixed maturities
Available-for-sale securities:
Gross realized gains	1	0	1	0
Gross realized losses	0	0	0	0
Net realized gains (losses)	1	0	1	0
Other-than-temporary impairments on investments
Other -than-temporary impairments on investments	0	0	0	0
Indemnity \| Equity securities
Available-for-sale securities:
Gross realized gains	0	0	0	0
Gross realized losses	0	0	0	0
Net realized gains (losses)	0	0	0	0
Other-than-temporary impairments on investments
Other -than-temporary impairments on investments	0	0	0	0
Indemnity \| Common stock
Trading securities:
Gross realized gains	0	0	0	1
Gross realized losses	0	0	0	0
Increases in fair value(1)	0	2	0	3
Net realized gains (losses) gains	0	2	0	4
Exchange
Realized gains (losses) on investments
Net realized investment gains (losses)	190	167	500	354
Other-than-temporary impairments on investments
Other -than-temporary impairments on investments	9	0	10	0
Portion recognized in other comprehensive income	0	0	0	0
Net impairment losses recognized in earnings	9	0	10	0
Exchange \| Fixed maturities
Available-for-sale securities:
Gross realized gains	4	22	26	47
Gross realized losses	(20)	(6)	(25)	(12)
Net realized gains (losses)	(16)	16	1	35
Other-than-temporary impairments on investments
Other -than-temporary impairments on investments	1	0	2	0
Exchange \| Equity securities
Available-for-sale securities:
Gross realized gains	0	5	4	10
Gross realized losses	(9)	(5)	(9)	(7)
Net realized gains (losses)	(9)	0	(5)	3
Other-than-temporary impairments on investments
Other -than-temporary impairments on investments	8	0	8	0
Exchange \| Common stock
Trading securities:
Gross realized gains	90	37	246	122
Gross realized losses	(8)	(24)	(23)	(57)
Increases in fair value(1)	133	138	281	251
Net realized gains (losses) gains	$ 215	$ 151	$ 504	$ 316

This item represents the difference between the gross realized gains and losses realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

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This item represents the gross profit realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

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The amount by which the fair value of an investment in debt and equity securities categorized as Available-for-sale is less than the amortized cost basis or carrying amount of that investment at the balance sheet date and the decline in fair value is deemed to be other than temporary, before considering whether or not such amount is recognized in earnings or other comprehensive income.

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Amount before tax of other than temporary impairment (OTTI) on investment in available-for-sale debt security, recognized in other comprehensive loss.

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The amount of other than temporary impairment losses on investments in debt and equity securities categorized as Available-for-sale which have been recognized in earnings during the period. Such impairment losses consist of other than temporary impairments (OTTI) on equity securities, credit losses on investments in debt securities, and when the entity intends to sell an impaired debt security or it is more likely than not that the entity will be required to sell the impaired debt security before recovery of its amortized cost basis.

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The net realized gains or losses on investments during the period, not including gains or losses on securities separately or otherwise categorized as trading, available-for-sale, or held-to-maturity.

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