Postretirement benefits Components of net periodic benefit costs (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans
Service cost	$ 1	$ 1	$ 2	$ 2
Non-service (benefit) cost	(52)	(35)	(103)	(69)
Net periodic benefit cost (benefit)	(51)	(34)	(101)	(67)
Other Postretirement Benefits Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans
Service cost	0	0	0	0
Interest cost	0	0	0	1
Expected return on plan assets	0	(1)	0	(2)
Defined Benefit Plan, Amortization of Gain (Loss)	0	0	0	0
Amortization of prior service cost	(6)	(20)	(26)	(40)
Settlements	0	0	0	0
Non-service (benefit) cost	(6)	(21)	(26)	(41)
Net periodic benefit cost (benefit)	(6)	(21)	(26)	(41)
Losses and loss expenses | Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans
Service cost	0	0	0	0
Non-service (benefit) cost	(4)	(3)	(9)	(6)
Losses and loss expenses | Other Postretirement Benefits Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans
Service cost	0	0	0	0
Non-service (benefit) cost	(1)	(2)	(3)	(4)
Administrative Expense | Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans
Service cost	1	1	2	2
Non-service (benefit) cost	(48)	(32)	(94)	(63)
Administrative Expense | Other Postretirement Benefits Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans
Service cost	0	0	0	0
Non-service (benefit) cost	(5)	(19)	(23)	(37)
Foreign Plan [Member] | Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans
Service cost	1	1	2	2
Interest cost	4	5	9	11
Expected return on plan assets	(11)	(11)	(22)	(21)
Defined Benefit Plan, Amortization of Gain (Loss)	1	1	2	1
Amortization of prior service cost	0	0	0	0
Settlements	0	0	0	0
Non-service (benefit) cost	(6)	(5)	(11)	(9)
Net periodic benefit cost (benefit)	(5)	(4)	(9)	(7)
UNITED STATES | Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans
Service cost	0	0	0	0
Interest cost	17	25	35	50
Expected return on plan assets	(63)	(56)	(127)	(112)
Defined Benefit Plan, Amortization of Gain (Loss)	0	0	0	0
Amortization of prior service cost	0	0	0	0
Settlements	0	1	0	2
Non-service (benefit) cost	(46)	(30)	(92)	(60)
Net periodic benefit cost (benefit)	$ (46)	$ (30)	$ (92)	$ (60)