Investment gains/losses (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Gain (Loss) on Investments [Line Items]
OTTI losses	$ (82)	$ (26)	$ (697)
Investment gains/losses	7,553	9,373	3,575
Fixed Maturities [Member]
Gain (Loss) on Investments [Line Items]
Gross gains from sales, redemptions and other disposals	58	104	360
Gross losses from sales, redemptions and other disposals	(50)	(171)	(89)
Equity Securities [Member]
Gain (Loss) on Investments [Line Items]
Gross gains from sales, redemptions and other disposals	7,853	9,526	4,016
Gross losses from sales, redemptions and other disposals	(334)	(103)	(125)
Other Types of Investments [Member]
Gain (Loss) on Investments [Line Items]
Other investment gains/losses	$ 108	$ 43	$ 110