Income taxes - Income tax expense components (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income tax expense:
Federal	$ 7,796	$ 9,253	$ 6,447
State	556	578	560
Foreign	888	701	928
Total income taxes	9,240	10,532	7,935
Income tax expense:
Current	6,565	5,426	3,302
Deferred	2,675	5,106	4,633
Total income taxes	$ 9,240	$ 10,532	$ 7,935