Income taxes - Income tax expense reconciliation (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income tax expense reconciliation
Earnings before income taxes	$ 23,838	$ 33,667	$ 34,946
Hypothetical income tax expense computed at the U.S. federal statutory rate	8,343	11,783	12,231
Dividends received deduction and tax exempt interest	(905)	(789)	(1,146)
State income taxes, less U.S. federal income tax benefit	465	361	374
Foreign tax rate differences	(339)	(421)	(459)
U.S. income tax credits	(636)	(518)	(461)
Non-taxable exchange of investments		(1,143)
Net benefit from the enactment of the TCJA	(28,200)
Other differences, net	(243)	(33)	(7)
Total income taxes	$ (21,515)	$ 9,240	$ 10,532