Postretirement benefits Components of net periodic benefit costs (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans
Service cost	$ 1	$ 1
Non-service cost (benefit)	(51)	(34)
Net periodic benefit cost (benefit)	(50)	(33)
Other Postretirement Benefits Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans
Service cost	0	0
Interest cost	0	1
Expected return on plan assets	0	(1)
Defined Benefit Plan, Amortization of Gain (Loss)	0	0
Amortization of prior service cost	(20)	(20)
Settlements	0	0
Non-service cost (benefit)	(20)	(20)
Net periodic benefit cost (benefit)	(20)	(20)
Losses and loss expenses | Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans
Service cost	0	0
Non-service cost (benefit)	(5)	(3)
Losses and loss expenses | Other Postretirement Benefits Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans
Service cost	0	0
Non-service cost (benefit)	(2)	(2)
Administrative Expense | Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans
Service cost	1	1
Non-service cost (benefit)	(46)	(31)
Administrative Expense | Other Postretirement Benefits Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans
Service cost	0	0
Non-service cost (benefit)	(18)	(18)
Foreign Plan [Member] | Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans
Service cost	1	1
Interest cost	5	6
Expected return on plan assets	(11)	(10)
Defined Benefit Plan, Amortization of Gain (Loss)	1	0
Amortization of prior service cost	0	0
Settlements	0	0
Non-service cost (benefit)	(5)	(4)
Net periodic benefit cost (benefit)	(4)	(3)
UNITED STATES | Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans
Service cost	0	0
Interest cost	18	25
Expected return on plan assets	(64)	(56)
Defined Benefit Plan, Amortization of Gain (Loss)	0	0
Amortization of prior service cost	0	0
Settlements	0	1
Non-service cost (benefit)	(46)	(30)
Net periodic benefit cost (benefit)	$ (46)	$ (30)