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Postretirement benefits (Narrative) (Details) - USD ($) $ in Millions |  | 12 Months Ended
--- | --- | ---
Oct. 31, 2016 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Expenses recognized during period under the defined contributions plans |  | $ 171 | $ 171 | $ 166
Available for sale, Fair Value |  | $ 85,488 | 78,470 |
Minimum |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Percentage |  | 55.00% |  |
Maximum |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Percentage |  | 65.00% |  |
Pension Plan [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Accumulated Benefit Obligation |  | $ 4,600 | 4,000 |
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year |  | 23 |  |
Other Postretirement Benefits Plan [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Plan Assets, Amount |  | 152 | 143 | 157
Actuarial Loss (gain) |  | 3 | (20) |
Defined Benefit Plan, Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Accumulated Benefit Obligation |  | 25 | 23 |
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year |  | 1 |  |
Defined Benefit Plan, Plan Amendment [Abstract] |  |  |  |
(Increase) decrease in other comprehensive income, curtailment |  | 0 | 3 | 39
Amortization of Prior Service Cost (Credit) |  | 84 | 85 | 89
UNITED STATES | Pension Plan [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Plan Assets, Amount |  | 3,301 | 2,784 | 3,109
Actuarial Loss (gain) |  | 443 | (214) |
Defined Benefit Plan, Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Accumulated Benefit Obligation |  | 3,569 | 3,066 |
Defined Benefit Plan, Plan Amendment [Abstract] |  |  |  |
(Increase) decrease in other comprehensive income, curtailment |  | 0 | 0 | 0
Amortization of Prior Service Cost (Credit) |  | 0 | 0 | 0
UNITED STATES | Postretirement Health Coverage [Member] |  |  |  |
Defined Benefit Plan, Plan Amendment [Abstract] |  |  |  |
Effect of Plan Amendment on Accumulated Benefit Obligation | $ 383 |  |  |
Amortization of Prior Service Cost (Credit) |  | 79 | 80 | 89
Remaining Balance of Change in Benefit Obligation For Plan Amendment |  | 105 |  |
UNITED STATES | Postretirement Health Coverage [Member] | Subject to Amortization [Member] |  |  |  |
Defined Benefit Plan, Plan Amendment [Abstract] |  |  |  |
Effect of Plan Amendment on Accumulated Benefit Obligation | $ 410 |  |  |
UNITED STATES | Level 3 | Pension Plan [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Available for sale, Fair Value |  | 0 |  |
Non - U.S. | Pension Plan [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Plan Assets, Amount |  | 1,141 | 1,008 | 1,172
Actuarial Loss (gain) |  | 124 | (71) |
Defined Benefit Plan, Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Accumulated Benefit Obligation |  | 173 | 115 |
Defined Benefit Plan, Plan Amendment [Abstract] |  |  |  |
(Increase) decrease in other comprehensive income, curtailment |  | (3) | 0 | (6)
Amortization of Prior Service Cost (Credit) |  | $ 0 | $ 0 | $ 0

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