Investments (Details 5) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Realized gains (losses) on investments
Net realized investment gains (losses)	$ 169	$ (422)	$ 358	$ (234)
Net impairment losses recognized in earnings	0	0	0	0
Indemnity
Realized gains (losses) on investments
Net realized investment gains (losses)	2	(6)	4	1
Indemnity \| Fixed maturities
Available-for-sale securities:
Gross realized gains	0	0	0	2
Gross realized losses	0	0	0	0
Net realized gains	0	0	0	2
Indemnity \| Equity securities
Available-for-sale securities:
Gross realized gains	0	0	0	3
Gross realized losses	0	0	0	0
Net realized gains	0	0	0	3
Indemnity \| Common stock
Trading securities:
Gross realized gains	0	0	1	2
Gross realized losses	0	0	0	0
Valuation adjustments	2	(6)	3	(6)
Net realized (losses) gains	2	(6)	4	(4)
Exchange
Realized gains (losses) on investments
Net realized investment gains (losses)	167	(416)	354	(235)
Net impairment losses recognized in earnings		0.3	0.1	0.3
Exchange \| Fixed maturities
Available-for-sale securities:
Gross realized gains	22	15	47	66
Gross realized losses	(6)	(5)	(12)	(22)
Net realized gains	16	10	35	44
Exchange \| Equity securities
Available-for-sale securities:
Gross realized gains	5	3	10	19
Gross realized losses	(5)	0	(7)	(1)
Net realized gains	0	3	3	18
Exchange \| Common stock
Trading securities:
Gross realized gains	37	56	122	183
Gross realized losses	(24)	(35)	(57)	(59)
Valuation adjustments	138	(450)	251	(421)
Net realized (losses) gains	$ 151	$ (429)	$ 316	$ (297)

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 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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