Income taxes - Income tax expense reconciliation (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income tax expense reconciliation
Earnings before income taxes	$ 34,946	$ 28,105	$ 28,796
Hypothetical income tax expense computed at the U.S. federal statutory rate	12,231	9,837	10,079
Dividends received deduction and tax exempt interest	(1,146)	(820)	(514)
State income taxes, less U.S. federal income tax benefit	374	364	168
Foreign tax rate differences	(459)	(252)	(256)
U.S. income tax credits	(461)	(333)	(457)
Non-taxable exchange of investments		(679)
Other differences, net	(7)	(182)	(69)
Total income taxes	$ 10,532	$ 7,935	$ 8,951