Postretirement benefits Schedule of net periodic benefit costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
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	$ 76	$ 321	$ 16
Pension Plan [Member]
Defined Benefit Plan, Amount Recognized in Net Periodic Benefit Cost (Credit) and Other Comprehensive (Income) Loss, before Tax [Abstract]
Service Cost	60	69	80
Defined Benefit Plan, Non Service (Benefit) Cost	(84)	(124)	(123)
Net Periodic Benefit Cost	(24)	(55)	(43)
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	1	2
Interest Cost	4	3	4
Expected Return on Plan Assets	(4)	(5)	(5)
Amortization of (Gains) Losses	0	0	0
Amortization of Prior Service Cost (Credit)	(84)	(85)	(89)
Recognized Net (Gain) Loss Due to Curtailments	0	(2)	(37)
Recognized Net (Gain) Loss Due to Settlements	0	0	0
Defined Benefit Plan, Non Service (Benefit) Cost	(84)	(89)	(127)
Net Periodic Benefit Cost	(84)	(88)	(125)
(Increase) decrease in Other Comprehensive Income (Loss), Net Actuarial (Gain) Loss)	(2)	(11)	(3)
Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), before Tax	0	0	(23)
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, before Tax	0	(1)	0
Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, before Tax	84	85	89
(Increase) decrease in other comprehensive income, curtailment	0	3	39
(Increase) decrease in other comprehensive income, settlement	0	0	0
Total (increase) decrease in other comprehensive (Income) Loss	82	76	102
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	6	7	7
Defined Benefit Plan, Non Service (Benefit) Cost	(7)	(10)	(8)
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	(8)	(9)	(13)
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	54	62	73
Defined Benefit Plan, Non Service (Benefit) Cost	(77)	(114)	(115)
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	0	1	2
Defined Benefit Plan, Non Service (Benefit) Cost	(76)	(80)	(114)
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	11	12	17
Interest Cost	27	27	27
Expected Return on Plan Assets	(45)	(50)	(42)
Amortization of (Gains) Losses	3	1	3
Amortization of Prior Service Cost (Credit)	0	0	0
Recognized Net (Gain) Loss Due to Curtailments	(1)	0	(27)
Recognized Net (Gain) Loss Due to Settlements	1	3	0
Defined Benefit Plan, Non Service (Benefit) Cost	(15)	(19)	(39)
Net Periodic Benefit Cost	(4)	(7)	(22)
(Increase) decrease in Other Comprehensive Income (Loss), Net Actuarial (Gain) Loss)	6	34	(57)
Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), before Tax	1	3	0
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, before Tax	(3)	(1)	(3)
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	(3)	0	(6)
(Increase) decrease in other comprehensive income, settlement	(1)	(3)	0
Total (increase) decrease in other comprehensive (Income) Loss	0	33	(66)
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	49	57	63
Interest Cost	118	105	105
Expected Return on Plan Assets	(189)	(212)	(189)
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	2	2	0
Defined Benefit Plan, Non Service (Benefit) Cost	(69)	(105)	(84)
Net Periodic Benefit Cost	(20)	(48)	(21)
(Increase) decrease in Other Comprehensive Income (Loss), Net Actuarial (Gain) Loss)	(4)	214	(21)
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	(2)	(2)	1
Total (increase) decrease in other comprehensive (Income) Loss	$ (6)	$ 212	$ (20)