Investment gains/losses (Detail) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Gain (Loss) on Investments [Line Items]
OTTI losses	$ (26)	$ (678)	$ (26)	$ (697)
Investment gains/losses	8,266	(376)	8,725	3,121
Fixed Maturities [Member]
Gain (Loss) on Investments [Line Items]
Gross gains	6	4	88	233
Gross losses	(44)	(25)	(128)	(73)
Equity Securities [Member]
Gain (Loss) on Investments [Line Items]
Gross gains	8,407	354	8,855	3,749
Gross losses	(75)	(38)	(95)	(41)
Other Types of Investments [Member]
Gain (Loss) on Investments [Line Items]
Other investment gains/losses	$ (2)	$ 7	$ 31	$ (50)

- Definition

This item represents the net total realized and unrealized gain (loss) included in earnings for the period as a result of selling or holding marketable securities categorized as trading, available-for-sale, or held-to-maturity, including the unrealized holding gain (loss) of held-to-maturity securities transferred to the trading security category and the cumulative unrealized gain (loss) which was included in other comprehensive income (a separate component of shareholders' equity) for available-for-sale securities transferred to trading securities during the period. Additionally, this item would include any gains (losses) realized during the period from the sale of investments accounted for under the cost method of accounting and losses recognized for other than temporary impairments (OTTI) of the subject investments.

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