Postretirement benefits Schedule of net periodic benefit costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan, Amount Recognized in Net Periodic Benefit Cost (Credit) and Other Comprehensive (Income) Loss, before Tax [Abstract]
Total (increase) decrease in other comprehensive (Income) Loss	$ 232	$ 76	$ 321
Pension Plan [Member]
Defined Benefit Plan, Amount Recognized in Net Periodic Benefit Cost (Credit) and Other Comprehensive (Income) Loss, before Tax [Abstract]
Service Cost	4	60	69
Defined Benefit Plan, Non Service (Benefit) Cost	(140)	(84)	(124)
Net Periodic Benefit Cost	(136)	(24)	(55)
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan, Amount Recognized in Net Periodic Benefit Cost (Credit) and Other Comprehensive (Income) Loss, before Tax [Abstract]
Service Cost	1	0	1
Interest Cost	2	4	3
Expected Return on Plan Assets	(5)	(4)	(5)
Amortization of (Gains) Losses	0	0	0
Amortization of Prior Service Cost (Credit)	(83)	(84)	(85)
Recognized Net (Gain) Loss Due to Curtailments	0	0	(2)
Recognized Net (Gain) Loss Due to Settlements	0	0	0
Defined Benefit Plan, Non Service (Benefit) Cost	(86)	(84)	(89)
Net Periodic Benefit Cost	(85)	(84)	(88)
(Increase) decrease in Other Comprehensive Income (Loss), Net Actuarial (Gain) Loss)	(2)	(2)	(11)
Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), before Tax	0	0	0
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, before Tax	0	0	(1)
Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, before Tax	83	84	85
(Increase) decrease in other comprehensive income, curtailment	0	0	3
(Increase) decrease in other comprehensive income, settlement	0	0	0
Total (increase) decrease in other comprehensive (Income) Loss	81	82	76
Losses and loss expenses [Member] | Pension Plan [Member]
Defined Benefit Plan, Amount Recognized in Net Periodic Benefit Cost (Credit) and Other Comprehensive (Income) Loss, before Tax [Abstract]
Service Cost	0	6	7
Defined Benefit Plan, Non Service (Benefit) Cost	(12)	(7)	(10)
Losses and loss expenses [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan, Amount Recognized in Net Periodic Benefit Cost (Credit) and Other Comprehensive (Income) Loss, before Tax [Abstract]
Service Cost	0	0	0
Defined Benefit Plan, Non Service (Benefit) Cost	(9)	(8)	(9)
General and Administrative Expense [Member] | Pension Plan [Member]
Defined Benefit Plan, Amount Recognized in Net Periodic Benefit Cost (Credit) and Other Comprehensive (Income) Loss, before Tax [Abstract]
Service Cost	4	54	62
Defined Benefit Plan, Non Service (Benefit) Cost	(128)	(77)	(114)
General and Administrative Expense [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan, Amount Recognized in Net Periodic Benefit Cost (Credit) and Other Comprehensive (Income) Loss, before Tax [Abstract]
Service Cost	1	0	1
Defined Benefit Plan, Non Service (Benefit) Cost	(77)	(76)	(80)
Non - U.S. | Pension Plan [Member]
Defined Benefit Plan, Amount Recognized in Net Periodic Benefit Cost (Credit) and Other Comprehensive (Income) Loss, before Tax [Abstract]
Service Cost	4	11	12
Interest Cost	22	27	27
Expected Return on Plan Assets	(41)	(45)	(50)
Amortization of (Gains) Losses	2	3	1
Amortization of Prior Service Cost (Credit)	0	0	0
Recognized Net (Gain) Loss Due to Curtailments	(1)	(1)	0
Recognized Net (Gain) Loss Due to Settlements	0	1	3
Defined Benefit Plan, Non Service (Benefit) Cost	(18)	(15)	(19)
Net Periodic Benefit Cost	(14)	(4)	(7)
(Increase) decrease in Other Comprehensive Income (Loss), Net Actuarial (Gain) Loss)	56	6	34
Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), before Tax	0	1	3
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, before Tax	(2)	(3)	(1)
Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, before Tax	(1)	0	0
(Increase) decrease in other comprehensive income, curtailment	(1)	(3)	0
(Increase) decrease in other comprehensive income, settlement	0	(1)	(3)
Total (increase) decrease in other comprehensive (Income) Loss	52	0	33
UNITED STATES | Pension Plan [Member]
Defined Benefit Plan, Amount Recognized in Net Periodic Benefit Cost (Credit) and Other Comprehensive (Income) Loss, before Tax [Abstract]
Service Cost	0	49	57
Interest Cost	99	118	105
Expected Return on Plan Assets	(224)	(189)	(212)
Amortization of (Gains) Losses	0	0	0
Amortization of Prior Service Cost (Credit)	0	0	0
Recognized Net (Gain) Loss Due to Curtailments	0	0	0
Recognized Net (Gain) Loss Due to Settlements	3	2	2
Defined Benefit Plan, Non Service (Benefit) Cost	(122)	(69)	(105)
Net Periodic Benefit Cost	(122)	(20)	(48)
(Increase) decrease in Other Comprehensive Income (Loss), Net Actuarial (Gain) Loss)	102	(4)	214
Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), before Tax	0	0	0
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, before Tax	0	0	0
Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, before Tax	0	0	0
(Increase) decrease in other comprehensive income, curtailment	0	0	0
(Increase) decrease in other comprehensive income, settlement	(3)	(2)	(2)
Total (increase) decrease in other comprehensive (Income) Loss	$ 99	$ (6)	$ 212