Income taxes - Provision for income taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
U.S. federal - Current	$ 483	$ 979	$ 2,101
Non-U.S. - Current	135	225	173
U.S. state - Current	12	7	12
Total current income tax expense (benefit)	630	1,211	2,286
U.S. federal - Deferred	25	(98)	51
Non-U.S. - Deferred	56	(8)	61
U.S. state - Deferred	0	1	0
Total deferred income tax expense (benefit)	81	(105)	112
Total U.S. federal income taxes	508	881	2,152
Total Non-U.S. income taxes	191	217	234
Total U.S. state income taxes	12	8	12
Provision for income taxes	$ 711	$ 1,106	$ 2,398