Postemployment benefit plans (Details 5) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
U.S. Pension Benefits
Change in Fair Value of Plan Assets
Fair value of plan assets, beginning of year	$ 11,440	$ 12,530
Fair value of plan assets, end of year	11,354	11,440
U.S. Pension Benefits | Real estate
Change in Fair Value of Plan Assets
Fair value of plan assets, beginning of year	9
Fair value of plan assets, end of year	10	9
U.S. Pension Benefits | Level 3
Change in Fair Value of Plan Assets
Fair value of plan assets, beginning of year	59
Fair value of plan assets, end of year	57	59
U.S. Pension Benefits | Level 3 | Equities
Change in Fair Value of Plan Assets
Fair value of plan assets, beginning of year	5	9
Unrealized gains (losses)	0	(1)
Realized gains (losses)	0	1
Purchases, issuances and settlements	1	(4)
Transfers in and/or out of Level 3	(1)	0
Fair value of plan assets, end of year	5	5
U.S. Pension Benefits | Level 3 | Fixed income securities
Change in Fair Value of Plan Assets
Fair value of plan assets, beginning of year	42	29
Unrealized gains (losses)	4	(1)
Realized gains (losses)	(5)	0
Purchases, issuances and settlements	(9)	16
Transfers in and/or out of Level 3	(1)	(2)
Fair value of plan assets, end of year	31	42
U.S. Pension Benefits | Level 3 | Real estate
Change in Fair Value of Plan Assets
Fair value of plan assets, beginning of year	9	9
Unrealized gains (losses)	1	0
Realized gains (losses)	0	0
Purchases, issuances and settlements	0	0
Transfers in and/or out of Level 3	0	0
Fair value of plan assets, end of year	10	9
U.S. Pension Benefits | Level 3 | Other
Change in Fair Value of Plan Assets
Fair value of plan assets, beginning of year	3	0
Unrealized gains (losses)	0	0
Realized gains (losses)	0	0
Purchases, issuances and settlements	8	2
Transfers in and/or out of Level 3	0	1
Fair value of plan assets, end of year	11	3
Non-U.S. Pension Benefits
Change in Fair Value of Plan Assets
Fair value of plan assets, beginning of year	3,890	4,100
Fair value of plan assets, end of year	3,887	3,890
Non-U.S. Pension Benefits | Real estate
Change in Fair Value of Plan Assets
Fair value of plan assets, beginning of year	172
Fair value of plan assets, end of year	179	172
Non-U.S. Pension Benefits | Level 3
Change in Fair Value of Plan Assets
Fair value of plan assets, beginning of year	7
Fair value of plan assets, end of year	2	7
Non-U.S. Pension Benefits | Level 3 | Equities
Change in Fair Value of Plan Assets
Fair value of plan assets, beginning of year	2	0
Unrealized gains (losses)	0	0
Realized gains (losses)	(1)	0
Purchases, issuances and settlements	(1)	0
Transfers in and/or out of Level 3	0	2
Fair value of plan assets, end of year	0	2
Non-U.S. Pension Benefits | Level 3 | Fixed income securities
Change in Fair Value of Plan Assets
Fair value of plan assets, beginning of year	5	11
Unrealized gains (losses)	0	(1)
Realized gains (losses)	0	0
Purchases, issuances and settlements	(1)	0
Transfers in and/or out of Level 3	(2)	(5)
Fair value of plan assets, end of year	2	5
Non-U.S. Pension Benefits | Level 3 | Real estate
Change in Fair Value of Plan Assets
Fair value of plan assets, beginning of year	0	39
Unrealized gains (losses)	0	(17)
Realized gains (losses)	0	15
Purchases, issuances and settlements	0	(37)
Transfers in and/or out of Level 3	0	0
Fair value of plan assets, end of year	0	0
Non-U.S. Pension Benefits | Level 3 | Other
Change in Fair Value of Plan Assets
Fair value of plan assets, beginning of year	0	0
Unrealized gains (losses)	0	0
Realized gains (losses)	0	0
Purchases, issuances and settlements	0	0
Transfers in and/or out of Level 3	0	0
Fair value of plan assets, end of year	0	0
Other Postretirement Benefits
Change in Fair Value of Plan Assets
Fair value of plan assets, beginning of year	650	776
Fair value of plan assets, end of year	550	650
Other Postretirement Benefits | Level 3
Change in Fair Value of Plan Assets
Fair value of plan assets, beginning of year	0
Fair value of plan assets, end of year	$ 0	$ 0