Income taxes - Income tax expense reconciliation (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income tax expense reconciliation
Earnings before income taxes	$ 102,696	$ 4,001	$ 23,838
Hypothetical income tax expense computed at the U.S. federal statutory rate	21,566	840	8,343
Dividends received deduction and tax-exempt interest	(433)	(393)	(905)
State income taxes, less U.S. federal income tax benefit	494	138	465
Foreign tax rate differences	(6)	271	(339)
U.S. income tax credits	(942)	(711)	(636)
Net benefit from the enactment of the TCJA		(302)	(28,200)
Other differences, net	225	(164)	(243)
Total income taxes	$ 20,904	$ (321)	$ (21,515)