Investment gains/losses (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Gain (Loss) on Investments [Line Items]
OTTI losses	$ (26)	$ (697)	$ (228)
Investment gains/losses	9,373	3,575	4,065
Fixed Maturities [Member]
Gain (Loss) on Investments [Line Items]
Gross gains from sales, redemptions and other disposals	104	360	1,783
Gross losses from sales, redemptions and other disposals	(171)	(89)	(139)
Equity Securities [Member]
Gain (Loss) on Investments [Line Items]
Gross gains from sales, redemptions and other disposals	9,526	4,016	1,253
Gross losses from sales, redemptions and other disposals	(103)	(125)	(62)
Other Types of Investments [Member]
Gain (Loss) on Investments [Line Items]
Other investment gains/losses	$ 43	$ 110	$ 1,458