Income taxes - Income tax expense reconciliation (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income tax expense reconciliation
Earnings before income taxes	$ 55,693	$ 102,696	$ 4,001
Hypothetical income tax expense computed at the U.S. federal statutory rate	11,696	21,566	840
Dividends received deduction and tax-exempt interest	(448)	(433)	(393)
State income taxes, less U.S. federal income tax benefit	858	494	138
Foreign tax rate differences	13	(6)	271
U.S. income tax credits	(1,519)	(942)	(711)
Net benefit from the enactment of the TCJA			(302)
Goodwill impairments	1,977	20	21
Other differences, net	(137)	205	(185)
Total income taxes	$ 12,440	$ 20,904	$ (321)
Effective income tax rate	22.30%	20.40%	(8.00%)