Income taxes (Provision for Income Taxes) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current provision:
Federal	$ 8,615	$ 984	$ 1,129
State	5	65	40
Foreign	275	176	272
Total current provision	8,895	1,225	1,441
Deferred (benefit) provision:
Federal	(1,120)	372	(290)
State	0	(69)	(78)
Foreign	(157)	(87)	(34)
Total deferred (benefit) provision	(1,277)	216	(402)
Total provision for income taxes	$ 7,618	$ 1,441	$ 1,039