Postemployment benefit plans (Details 6) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
U.S. pensions
Defined Benefit Plan Disclosure
Fair value of plan assets	$ 15,994	$ 12,697	$ 13,416
U.S. pensions | U.S. equities
Defined Benefit Plan Disclosure
Fair value of plan assets	2,734	2,161
U.S. pensions | Non-U.S. equities
Defined Benefit Plan Disclosure
Fair value of plan assets	2,068	1,280
U.S. pensions | U.S. corporate bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	6,634	6,484
U.S. pensions | Non-U.S. corporate bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	1,414	1,332
U.S. pensions | U.S. government bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	2,220	590
U.S. pensions | U.S. governmental agency mortgage-backed securities
Defined Benefit Plan Disclosure
Fair value of plan assets	63	384
U.S. pensions | Non-U.S. government bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	96	79
U.S. pensions | Real estate
Defined Benefit Plan Disclosure
Fair value of plan assets	10	10
U.S. pensions | Cash, short-term instruments and other
Defined Benefit Plan Disclosure
Fair value of plan assets	755	377
U.S. pensions | Level 1
Defined Benefit Plan Disclosure
Fair value of plan assets	4,876	3,452
U.S. pensions | Level 1 | U.S. equities
Defined Benefit Plan Disclosure
Fair value of plan assets	2,578	1,971
U.S. pensions | Level 1 | Non-U.S. equities
Defined Benefit Plan Disclosure
Fair value of plan assets	2,068	1,279
U.S. pensions | Level 1 | U.S. corporate bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
U.S. pensions | Level 1 | Non-U.S. corporate bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
U.S. pensions | Level 1 | U.S. government bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
U.S. pensions | Level 1 | U.S. governmental agency mortgage-backed securities
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
U.S. pensions | Level 1 | Non-U.S. government bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
U.S. pensions | Level 1 | Real estate
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
U.S. pensions | Level 1 | Cash, short-term instruments and other
Defined Benefit Plan Disclosure
Fair value of plan assets	230	202
U.S. pensions | Level 2
Defined Benefit Plan Disclosure
Fair value of plan assets	10,380	8,765
U.S. pensions | Level 2 | U.S. equities
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
U.S. pensions | Level 2 | Non-U.S. equities
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
U.S. pensions | Level 2 | U.S. corporate bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	6,577	6,371
U.S. pensions | Level 2 | Non-U.S. corporate bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	1,414	1,332
U.S. pensions | Level 2 | U.S. government bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	2,220	590
U.S. pensions | Level 2 | U.S. governmental agency mortgage-backed securities
Defined Benefit Plan Disclosure
Fair value of plan assets	63	384
U.S. pensions | Level 2 | Non-U.S. government bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	96	79
U.S. pensions | Level 2 | Real estate
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
U.S. pensions | Level 2 | Cash, short-term instruments and other
Defined Benefit Plan Disclosure
Fair value of plan assets	10	9
U.S. pensions | Level 3
Defined Benefit Plan Disclosure
Fair value of plan assets	90	107
U.S. pensions | Level 3 | U.S. equities
Defined Benefit Plan Disclosure
Fair value of plan assets	23	35
U.S. pensions | Level 3 | Non-U.S. equities
Defined Benefit Plan Disclosure
Fair value of plan assets	0	1
U.S. pensions | Level 3 | Fixed income securities
Defined Benefit Plan Disclosure
Fair value of plan assets	57	61	60
U.S. pensions | Level 3 | U.S. corporate bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	57	61
U.S. pensions | Level 3 | Non-U.S. corporate bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
U.S. pensions | Level 3 | U.S. government bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
U.S. pensions | Level 3 | U.S. governmental agency mortgage-backed securities
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
U.S. pensions | Level 3 | Non-U.S. government bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
U.S. pensions | Level 3 | Real estate
Defined Benefit Plan Disclosure
Fair value of plan assets	10	10	10
U.S. pensions | Level 3 | Cash, short-term instruments and other
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
U.S. pensions | Measured at NAV
Defined Benefit Plan Disclosure
Fair value of plan assets	648	373
U.S. pensions | Measured at NAV | U.S. equities
Defined Benefit Plan Disclosure
Fair value of plan assets	133	155
U.S. pensions | Measured at NAV | U.S. corporate bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	0	52
U.S. pensions | Measured at NAV | Cash, short-term instruments and other
Defined Benefit Plan Disclosure
Fair value of plan assets	515	166
Non-U.S. pensions
Defined Benefit Plan Disclosure
Fair value of plan assets	4,525	4,025	4,305
Non-U.S. pensions | U.S. equities
Defined Benefit Plan Disclosure
Fair value of plan assets	58	43
Non-U.S. pensions | Non-U.S. equities
Defined Benefit Plan Disclosure
Fair value of plan assets	440	340
Non-U.S. pensions | Global equities
Defined Benefit Plan Disclosure
Fair value of plan assets	153	136
Non-U.S. pensions | U.S. corporate bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	253	206
Non-U.S. pensions | Non-U.S. corporate bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	815	696
Non-U.S. pensions | U.S. government bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	65	74
Non-U.S. pensions | Non-U.S. government bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	1,952	1,721
Non-U.S. pensions | Global fixed income
Defined Benefit Plan Disclosure
Fair value of plan assets	390	476
Non-U.S. pensions | Real estate
Defined Benefit Plan Disclosure
Fair value of plan assets	211	185
Non-U.S. pensions | Cash, short-term instruments and other
Defined Benefit Plan Disclosure
Fair value of plan assets	188	148
Non-U.S. pensions | Level 1
Defined Benefit Plan Disclosure
Fair value of plan assets	498	391
Change to previously reported Non-U.S. Pension		(143)
Non-U.S. pensions | Level 1 | U.S. equities
Defined Benefit Plan Disclosure
Fair value of plan assets	58	43
Non-U.S. pensions | Level 1 | Non-U.S. equities
Defined Benefit Plan Disclosure
Fair value of plan assets	346	259
Non-U.S. pensions | Level 1 | Global equities
Defined Benefit Plan Disclosure
Fair value of plan assets	26	23
Non-U.S. pensions | Level 1 | U.S. corporate bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Non-U.S. pensions | Level 1 | Non-U.S. corporate bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Non-U.S. pensions | Level 1 | U.S. government bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Non-U.S. pensions | Level 1 | Non-U.S. government bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Non-U.S. pensions | Level 1 | Global fixed income
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Non-U.S. pensions | Level 1 | Real estate
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Non-U.S. pensions | Level 1 | Cash, short-term instruments and other
Defined Benefit Plan Disclosure
Fair value of plan assets	68	66
Non-U.S. pensions | Level 2
Defined Benefit Plan Disclosure
Fair value of plan assets	3,636	3,270
Non-U.S. pensions | Level 2 | U.S. equities
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Non-U.S. pensions | Level 2 | Non-U.S. equities
Defined Benefit Plan Disclosure
Fair value of plan assets	29	28
Non-U.S. pensions | Level 2 | Global equities
Defined Benefit Plan Disclosure
Fair value of plan assets	16	23
Non-U.S. pensions | Level 2 | U.S. corporate bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	253	206
Non-U.S. pensions | Level 2 | Non-U.S. corporate bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	808	690
Non-U.S. pensions | Level 2 | U.S. government bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	65	74
Non-U.S. pensions | Level 2 | Non-U.S. government bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	1,952	1,721
Non-U.S. pensions | Level 2 | Global fixed income
Defined Benefit Plan Disclosure
Fair value of plan assets	182	261
Non-U.S. pensions | Level 2 | Real estate
Defined Benefit Plan Disclosure
Fair value of plan assets	211	185
Non-U.S. pensions | Level 2 | Cash, short-term instruments and other
Defined Benefit Plan Disclosure
Fair value of plan assets	120	82
Non-U.S. pensions | Level 3
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Non-U.S. pensions | Level 3 | U.S. equities
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Non-U.S. pensions | Level 3 | Non-U.S. equities
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Non-U.S. pensions | Level 3 | Global equities
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Non-U.S. pensions | Level 3 | U.S. corporate bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Non-U.S. pensions | Level 3 | Non-U.S. corporate bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Non-U.S. pensions | Level 3 | U.S. government bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Non-U.S. pensions | Level 3 | Non-U.S. government bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Non-U.S. pensions | Level 3 | Global fixed income
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Non-U.S. pensions | Level 3 | Real estate
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Non-U.S. pensions | Level 3 | Cash, short-term instruments and other
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Non-U.S. pensions | Measured at NAV
Defined Benefit Plan Disclosure
Fair value of plan assets	391	364
Change to previously reported Non-U.S. Pension		143
Non-U.S. pensions | Measured at NAV | U.S. equities
Defined Benefit Plan Disclosure
Fair value of plan assets		0
Non-U.S. pensions | Measured at NAV | Non-U.S. equities
Defined Benefit Plan Disclosure
Fair value of plan assets	65	53
Non-U.S. pensions | Measured at NAV | Global equities
Defined Benefit Plan Disclosure
Fair value of plan assets	111	90
Non-U.S. pensions | Measured at NAV | Non-U.S. corporate bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	7	6
Non-U.S. pensions | Measured at NAV | Global fixed income
Defined Benefit Plan Disclosure
Fair value of plan assets	208	215
Other postretirement benefits
Defined Benefit Plan Disclosure
Fair value of plan assets	255	328	$ 504
Other postretirement benefits | U.S. equities
Defined Benefit Plan Disclosure
Fair value of plan assets	119	152
Other postretirement benefits | Non-U.S. equities
Defined Benefit Plan Disclosure
Fair value of plan assets	56	64
Other postretirement benefits | U.S. corporate bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	33	45
Other postretirement benefits | Non-U.S. corporate bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	6	11
Other postretirement benefits | U.S. government bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	9	8
Other postretirement benefits | U.S. governmental agency mortgage-backed securities
Defined Benefit Plan Disclosure
Fair value of plan assets	16	25
Other postretirement benefits | Non-U.S. government bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	3	3
Other postretirement benefits | Cash, short-term instruments and other
Defined Benefit Plan Disclosure
Fair value of plan assets	13	20
Other postretirement benefits | Level 1
Defined Benefit Plan Disclosure
Fair value of plan assets	177	218
Other postretirement benefits | Level 1 | U.S. equities
Defined Benefit Plan Disclosure
Fair value of plan assets	119	151
Other postretirement benefits | Level 1 | Non-U.S. equities
Defined Benefit Plan Disclosure
Fair value of plan assets	56	64
Other postretirement benefits | Level 1 | U.S. corporate bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Other postretirement benefits | Level 1 | Non-U.S. corporate bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Other postretirement benefits | Level 1 | U.S. government bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Other postretirement benefits | Level 1 | U.S. governmental agency mortgage-backed securities
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Other postretirement benefits | Level 1 | Non-U.S. government bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Other postretirement benefits | Level 1 | Cash, short-term instruments and other
Defined Benefit Plan Disclosure
Fair value of plan assets	2	3
Other postretirement benefits | Level 2
Defined Benefit Plan Disclosure
Fair value of plan assets	68	94
Other postretirement benefits | Level 2 | U.S. equities
Defined Benefit Plan Disclosure
Fair value of plan assets	0	1
Other postretirement benefits | Level 2 | Non-U.S. equities
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Other postretirement benefits | Level 2 | U.S. corporate bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	33	45
Other postretirement benefits | Level 2 | Non-U.S. corporate bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	6	11
Other postretirement benefits | Level 2 | U.S. government bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	9	8
Other postretirement benefits | Level 2 | U.S. governmental agency mortgage-backed securities
Defined Benefit Plan Disclosure
Fair value of plan assets	16	25
Other postretirement benefits | Level 2 | Non-U.S. government bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	3	3
Other postretirement benefits | Level 2 | Cash, short-term instruments and other
Defined Benefit Plan Disclosure
Fair value of plan assets	1	1
Other postretirement benefits | Level 3
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Other postretirement benefits | Level 3 | U.S. equities
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Other postretirement benefits | Level 3 | Non-U.S. equities
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Other postretirement benefits | Level 3 | U.S. corporate bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Other postretirement benefits | Level 3 | Non-U.S. corporate bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Other postretirement benefits | Level 3 | U.S. government bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Other postretirement benefits | Level 3 | U.S. governmental agency mortgage-backed securities
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Other postretirement benefits | Level 3 | Non-U.S. government bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Other postretirement benefits | Level 3 | Cash, short-term instruments and other
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Other postretirement benefits | Measured at NAV
Defined Benefit Plan Disclosure
Fair value of plan assets	10	16
Other postretirement benefits | Measured at NAV | U.S. corporate bonds
Defined Benefit Plan Disclosure
Fair value of plan assets		0
Other postretirement benefits | Measured at NAV | Cash, short-term instruments and other
Defined Benefit Plan Disclosure
Fair value of plan assets	$ 10	$ 16