Income taxes - Income tax expense components (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income tax expense:
Federal	$ 19,069	$ (1,613)	$ (23,427)
State	625	175	894
Foreign	1,210	1,117	1,018
Total income taxes	20,904	(321)	(21,515)
Income tax expense:
Current	5,818	5,176	3,299
Deferred	15,086	(5,497)	(24,814)
Total income taxes	$ 20,904	$ (321)	$ (21,515)