Investment gains/losses (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Gain (Loss) on Investments [Line Items]
OTTI losses				$ (19)
Investment gains/losses	$ 362	$ 2,366	$ 459	3,497
Fixed Maturities [Member]
Gain (Loss) on Investments [Line Items]
Gross gains	53	39	82	229
Gross losses	(46)	(19)	(84)	(48)
Equity Securities [Member]
Gain (Loss) on Investments [Line Items]
Gross gains	342	2,391	448	3,395
Gross losses	(14)	(3)	(20)	(3)
Other Types of Investments [Member]
Gain (Loss) on Investments [Line Items]
Other investment gains/losses	$ 27	$ (42)	$ 33	$ (57)