Investments (Details 5) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2013	Mar. 31, 2012
Realized gains (losses) on investments
Net realized investment gains (losses)	$ 249	$ 296
Other-than-temporary impairments on investments
Net impairment losses recognized in earnings	0	0
Indemnity
Realized gains (losses) on investments
Net realized investment gains (losses)	0	3
Other-than-temporary impairments on investments
Net impairment losses recognized in earnings	0	0
Portion recognized in other comprehensive income	0	0
Indemnity \| Fixed maturities
Available-for-sale securities:
Gross realized gains	0	0
Gross realized losses	0	0
Net realized gains	0	0
Indemnity \| Equity securities
Available-for-sale securities:
Gross realized gains	0	0
Gross realized losses	0	0
Net realized gains	0	0
Indemnity \| Common stock
Trading securities:
Gross realized gains	0	1
Gross realized losses	0	0
Increases in fair value(1)	0	2
Net realized (losses) gains	0	3
Exchange
Realized gains (losses) on investments
Net realized investment gains (losses)	249	293
Other-than-temporary impairments on investments
Net impairment losses recognized in earnings	0.4	0.1
Portion recognized in other comprehensive income	0	0
Exchange \| Fixed maturities
Available-for-sale securities:
Gross realized gains	15	9
Gross realized losses	(2)	(3)
Net realized gains	13	6
Exchange \| Equity securities
Available-for-sale securities:
Gross realized gains	2	1
Gross realized losses	0	0
Net realized gains	2	1
Exchange \| Common stock
Trading securities:
Gross realized gains	102	41
Gross realized losses	(12)	(12)
Increases in fair value(1)	144	257
Net realized (losses) gains	$ 234	$ 286

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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Before tax amount of other than temporary impairment (OTTI) on a debt security, categorized as available-for-sale, recognized in other comprehensive income (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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