Income taxes - Provision for income taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
U.S. federal - Current	$ 979	$ 2,101	$ 1,289
Non-U.S. - Current	225	173	238
U.S. state - Current	7	12	10
Total current income tax expense (benefit)	1,211	2,286	1,537
U.S. federal - Deferred	(98)	51	(122)
Non-U.S. - Deferred	(8)	61	(80)
U.S. state - Deferred	1	0	0
Total deferred income tax expense (benefit)	(105)	112	(202)
Total U.S. federal income taxes	881	2,152	1,167
Total Non-U.S. income taxes	217	234	158
Total U.S. state income taxes	8	12	10
Provision for income taxes	$ 1,106	$ 2,398	$ 1,335