Pension and other postretirement employee benefit plans - Net Periodic Benefit Costs (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Pension plans, U.S.
Amortization:
Total defined contribution plans	$ 115	$ 110	$ 204	$ 218
Pension plans, Non-U.S.
Amortization:
Total defined contribution plans	86	87	169	167
Pension plans, U.S.
Components of net periodic benefit cost
Benefits earned during the period	85	70	170	140
Interest cost on benefit obligations	125	134	250	268
Expected return on plan assets	(233)	(246)	(465)	(492)
Amortization:
Net (gain)/loss	61	7	123	13
Prior service cost/(credit)	(8)	(12)	(17)	(22)
Net periodic defined benefit cost	30	(47)	61	(93)
Other defined benefit pension plans	4	4	7	7
Total defined benefit plans	34	(43)	68	(86)
Total pension and OPEB cost included in compensation expense	149	67	272	132
Pension plans, Non-U.S.
Components of net periodic benefit cost
Benefits earned during the period	10	8	19	17
Interest cost on benefit obligations	28	36	56	70
Expected return on plan assets	(37)	(45)	(75)	(89)
Amortization:
Net (gain)/loss	9	12	18	24
Prior service cost/(credit)	(1)	0	(1)	0
Net periodic defined benefit cost	9	11	17	22
Other defined benefit pension plans	0	1	5	3
Total defined benefit plans	9	12	22	25
Total pension and OPEB cost included in compensation expense	95	99	191	192
OPEB plans
Components of net periodic benefit cost
Benefits earned during the period	0	0	0	0
Interest cost on benefit obligations	8	9	16	18
Expected return on plan assets	(27)	(25)	(53)	(50)
Amortization:
Net (gain)/loss	0	0	0	0
Prior service cost/(credit)	0	0	0	0
Net periodic defined benefit cost	(19)	(16)	(37)	(32)
Total defined benefit plans	(19)	(16)	(37)	(32)
Total pension and OPEB cost included in compensation expense	$ (19)	$ (16)	$ (37)	$ (32)