Investment gains/losses (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Gain (Loss) on Investments [Line Items]
Investment gains/losses	$ 1,850	$ 97
Fixed Maturities [Member]
Gain (Loss) on Investments [Line Items]
Gross gains from sales, redemptions and other disposals	19	29
Gross losses from sales, redemptions and other disposals	(3)	(38)
Equity Securities [Member]
Gain (Loss) on Investments [Line Items]
Gross gains from sales, redemptions and other disposals	1,807	106
Gross losses from sales, redemptions and other disposals	(10)	(6)
Other Types of Investments [Member]
Gain (Loss) on Investments [Line Items]
Other investment gains/losses	$ 37	$ 6