Postemployment benefit plans (Details 4) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Level 2
Defined Benefit Plan Disclosure
Change to previously reported US Pension and Other Postretirement Benefits		$ 141
Level 3
Defined Benefit Plan Disclosure
Change to previously reported US Pension and Other Postretirement Benefits		9
Measured at NAV
Defined Benefit Plan Disclosure
Change to previously reported US Pension and Other Postretirement Benefits		132
U.S. Pension Benefits
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	$ 11,354	11,440	$ 12,530
U.S. Pension Benefits | U.S. equities
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	2,995	3,148
U.S. Pension Benefits | Non-U.S. equities
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	1,658	2,050
U.S. Pension Benefits | U.S. corporate bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	4,389	4,046
U.S. Pension Benefits | Non-U.S. corporate bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	710	575
U.S. Pension Benefits | U.S. government bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	647	526
U.S. Pension Benefits | U.S. governmental agency mortgage-backed securities
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	491	627
U.S. Pension Benefits | Non-U.S. government bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	90	65
U.S. Pension Benefits | Real estate
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	10	9
U.S. Pension Benefits | Cash, short-term instruments and other
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	364	394
U.S. Pension Benefits | Level 1
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	4,562	5,177
U.S. Pension Benefits | Level 1 | U.S. equities
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	2,816	2,976
U.S. Pension Benefits | Level 1 | Non-U.S. equities
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	1,653	2,044
U.S. Pension Benefits | Level 1 | U.S. corporate bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
U.S. Pension Benefits | Level 1 | Non-U.S. corporate bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
U.S. Pension Benefits | Level 1 | U.S. government bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
U.S. Pension Benefits | Level 1 | U.S. governmental agency mortgage-backed securities
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
U.S. Pension Benefits | Level 1 | Non-U.S. government bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
U.S. Pension Benefits | Level 1 | Real estate
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
U.S. Pension Benefits | Level 1 | Cash, short-term instruments and other
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	93	157
U.S. Pension Benefits | Level 2
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	6,290	5,698
U.S. Pension Benefits | Level 2 | U.S. equities
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
U.S. Pension Benefits | Level 2 | Non-U.S. equities
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	5	5
U.S. Pension Benefits | Level 2 | U.S. corporate bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	4,273	3,872
U.S. Pension Benefits | Level 2 | Non-U.S. corporate bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	710	575
U.S. Pension Benefits | Level 2 | U.S. government bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	647	526
U.S. Pension Benefits | Level 2 | U.S. governmental agency mortgage-backed securities
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	491	627
U.S. Pension Benefits | Level 2 | Non-U.S. government bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	90	65
U.S. Pension Benefits | Level 2 | Real estate
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
U.S. Pension Benefits | Level 2 | Cash, short-term instruments and other
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	74	28
U.S. Pension Benefits | Level 3
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	57	59
U.S. Pension Benefits | Level 3 | Equities
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	5	5	9
U.S. Pension Benefits | Level 3 | U.S. equities
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	5	4
U.S. Pension Benefits | Level 3 | Non-U.S. equities
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	1
U.S. Pension Benefits | Level 3 | Fixed income securities
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	31	42	29
U.S. Pension Benefits | Level 3 | U.S. corporate bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	31	42
U.S. Pension Benefits | Level 3 | Non-U.S. corporate bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
U.S. Pension Benefits | Level 3 | U.S. government bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
U.S. Pension Benefits | Level 3 | U.S. governmental agency mortgage-backed securities
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
U.S. Pension Benefits | Level 3 | Non-U.S. government bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
U.S. Pension Benefits | Level 3 | Real estate
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	10	9	9
U.S. Pension Benefits | Level 3 | Other
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	11	3	0
U.S. Pension Benefits | Level 3 | Cash, short-term instruments and other
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	11	3
U.S. Pension Benefits | Measured at NAV
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	445	506
U.S. Pension Benefits | Measured at NAV | U.S. equities
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	174	168
U.S. Pension Benefits | Measured at NAV | Non-U.S. equities
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
U.S. Pension Benefits | Measured at NAV | U.S. corporate bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	85	132
U.S. Pension Benefits | Measured at NAV | Non-U.S. corporate bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
U.S. Pension Benefits | Measured at NAV | U.S. government bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
U.S. Pension Benefits | Measured at NAV | U.S. governmental agency mortgage-backed securities
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
U.S. Pension Benefits | Measured at NAV | Non-U.S. government bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
U.S. Pension Benefits | Measured at NAV | Real estate
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
U.S. Pension Benefits | Measured at NAV | Cash, short-term instruments and other
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	186	206
Non-U.S. Pension Benefits
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	3,887	3,890	4,100
Non-U.S. Pension Benefits | U.S. equities
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	513	544
Non-U.S. Pension Benefits | Non-U.S. equities
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	796	834
Non-U.S. Pension Benefits | Global equities
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	156	204
Non-U.S. Pension Benefits | U.S. corporate bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	152	138
Non-U.S. Pension Benefits | Non-U.S. corporate bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	356	402
Non-U.S. Pension Benefits | U.S. government bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	44	64
Non-U.S. Pension Benefits | Non-U.S. government bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	1,172	1,083
Non-U.S. Pension Benefits | Global fixed income
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	420	341
Non-U.S. Pension Benefits | Real estate
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	179	172
Non-U.S. Pension Benefits | Cash, short-term instruments and other
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	99	108
Non-U.S. Pension Benefits | Level 1
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	1,219	1,322
Non-U.S. Pension Benefits | Level 1 | U.S. equities
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	405	426
Non-U.S. Pension Benefits | Level 1 | Non-U.S. equities
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	639	680
Non-U.S. Pension Benefits | Level 1 | Global equities
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	122	155
Non-U.S. Pension Benefits | Level 1 | U.S. corporate bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
Non-U.S. Pension Benefits | Level 1 | Non-U.S. corporate bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
Non-U.S. Pension Benefits | Level 1 | U.S. government bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
Non-U.S. Pension Benefits | Level 1 | Non-U.S. government bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
Non-U.S. Pension Benefits | Level 1 | Global fixed income
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
Non-U.S. Pension Benefits | Level 1 | Real estate
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
Non-U.S. Pension Benefits | Level 1 | Cash, short-term instruments and other
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	53	61
Non-U.S. Pension Benefits | Level 2
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	2,230	2,134
Non-U.S. Pension Benefits | Level 2 | U.S. equities
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
Non-U.S. Pension Benefits | Level 2 | Non-U.S. equities
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	38	29
Non-U.S. Pension Benefits | Level 2 | Global equities
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	34	49
Non-U.S. Pension Benefits | Level 2 | U.S. corporate bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	151	135
Non-U.S. Pension Benefits | Level 2 | Non-U.S. corporate bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	345	389
Non-U.S. Pension Benefits | Level 2 | U.S. government bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	44	64
Non-U.S. Pension Benefits | Level 2 | Non-U.S. government bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	1,172	1,083
Non-U.S. Pension Benefits | Level 2 | Global fixed income
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	221	166
Non-U.S. Pension Benefits | Level 2 | Real estate
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	179	172
Non-U.S. Pension Benefits | Level 2 | Cash, short-term instruments and other
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	46	47
Non-U.S. Pension Benefits | Level 3
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	2	7
Non-U.S. Pension Benefits | Level 3 | Equities
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	2	0
Non-U.S. Pension Benefits | Level 3 | U.S. equities
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
Non-U.S. Pension Benefits | Level 3 | Non-U.S. equities
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	2
Non-U.S. Pension Benefits | Level 3 | Global equities
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
Non-U.S. Pension Benefits | Level 3 | Fixed income securities
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	2	5	11
Non-U.S. Pension Benefits | Level 3 | U.S. corporate bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	1	3
Non-U.S. Pension Benefits | Level 3 | Non-U.S. corporate bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	1	2
Non-U.S. Pension Benefits | Level 3 | U.S. government bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
Non-U.S. Pension Benefits | Level 3 | Non-U.S. government bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
Non-U.S. Pension Benefits | Level 3 | Global fixed income
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
Non-U.S. Pension Benefits | Level 3 | Real estate
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0	39
Non-U.S. Pension Benefits | Level 3 | Other
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0	0
Non-U.S. Pension Benefits | Level 3 | Cash, short-term instruments and other
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
Non-U.S. Pension Benefits | Measured at NAV
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	436	427
Non-U.S. Pension Benefits | Measured at NAV | U.S. equities
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	108	118
Non-U.S. Pension Benefits | Measured at NAV | Non-U.S. equities
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	119	123
Non-U.S. Pension Benefits | Measured at NAV | Global equities
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
Non-U.S. Pension Benefits | Measured at NAV | U.S. corporate bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
Non-U.S. Pension Benefits | Measured at NAV | Non-U.S. corporate bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	10	11
Non-U.S. Pension Benefits | Measured at NAV | U.S. government bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
Non-U.S. Pension Benefits | Measured at NAV | Non-U.S. government bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
Non-U.S. Pension Benefits | Measured at NAV | Global fixed income
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	199	175
Non-U.S. Pension Benefits | Measured at NAV | Real estate
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
Non-U.S. Pension Benefits | Measured at NAV | Cash, short-term instruments and other
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
Other Postretirement Benefits
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	550	650	$ 776
Other Postretirement Benefits | U.S. equities
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	277	297
Other Postretirement Benefits | Non-U.S. equities
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	110	136
Other Postretirement Benefits | U.S. corporate bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	70	87
Other Postretirement Benefits | Non-U.S. corporate bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	17	18
Other Postretirement Benefits | U.S. government bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	16	31
Other Postretirement Benefits | U.S. governmental agency mortgage-backed securities
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	31	45
Other Postretirement Benefits | Non-U.S. government bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	4	4
Other Postretirement Benefits | Cash, short-term instruments and other
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	25	32
Other Postretirement Benefits | Level 1
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	391	449
Other Postretirement Benefits | Level 1 | U.S. equities
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	276	296
Other Postretirement Benefits | Level 1 | Non-U.S. equities
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	110	136
Other Postretirement Benefits | Level 1 | U.S. corporate bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
Other Postretirement Benefits | Level 1 | Non-U.S. corporate bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
Other Postretirement Benefits | Level 1 | U.S. government bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
Other Postretirement Benefits | Level 1 | U.S. governmental agency mortgage-backed securities
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
Other Postretirement Benefits | Level 1 | Non-U.S. government bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
Other Postretirement Benefits | Level 1 | Cash, short-term instruments and other
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	5	17
Other Postretirement Benefits | Level 2
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	139	197
Other Postretirement Benefits | Level 2 | U.S. equities
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	1	1
Other Postretirement Benefits | Level 2 | Non-U.S. equities
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
Other Postretirement Benefits | Level 2 | U.S. corporate bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	69	83
Other Postretirement Benefits | Level 2 | Non-U.S. corporate bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	17	18
Other Postretirement Benefits | Level 2 | U.S. government bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	16	31
Other Postretirement Benefits | Level 2 | U.S. governmental agency mortgage-backed securities
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	31	45
Other Postretirement Benefits | Level 2 | Non-U.S. government bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	4	4
Other Postretirement Benefits | Level 2 | Cash, short-term instruments and other
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	1	15
Other Postretirement Benefits | Level 3
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
Other Postretirement Benefits | Level 3 | U.S. equities
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
Other Postretirement Benefits | Level 3 | Non-U.S. equities
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
Other Postretirement Benefits | Level 3 | U.S. corporate bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
Other Postretirement Benefits | Level 3 | Non-U.S. corporate bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
Other Postretirement Benefits | Level 3 | U.S. government bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
Other Postretirement Benefits | Level 3 | U.S. governmental agency mortgage-backed securities
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
Other Postretirement Benefits | Level 3 | Non-U.S. government bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
Other Postretirement Benefits | Level 3 | Cash, short-term instruments and other
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
Other Postretirement Benefits | Measured at NAV
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	20	4
Other Postretirement Benefits | Measured at NAV | U.S. equities
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
Other Postretirement Benefits | Measured at NAV | Non-U.S. equities
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
Other Postretirement Benefits | Measured at NAV | U.S. corporate bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	1	4
Other Postretirement Benefits | Measured at NAV | Non-U.S. corporate bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
Other Postretirement Benefits | Measured at NAV | U.S. government bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
Other Postretirement Benefits | Measured at NAV | U.S. governmental agency mortgage-backed securities
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
Other Postretirement Benefits | Measured at NAV | Non-U.S. government bonds
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	0	0
Other Postretirement Benefits | Measured at NAV | Cash, short-term instruments and other
Defined Benefit Plan Disclosure
Total Assets, at Fair Value	$ 19	$ 0