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Postretirement benefits Schedule of Allocation of Plan Assets (Details) - USD ($) $ in Millions | Dec. 31, 2017 | Dec. 31, 2016
--- | --- | ---
Defined Benefit Plan Disclosure [Line Items] |  |
Short-term investments | $ 3,561 | $ 3,002
Available for sale, Fair Value | 78,939 | 80,115
Equity securities | 937 | 814
Other investments | 4,672 | 4,519
Other Investments [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Other investments | 15 | 25
Pension Plan [Member] | UNITED STATES |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Short-term investments | 61 | 43
Equity securities | 1,154 | 728
Derivative Instruments Fair Value |  | 3
Defined benefit plan, fair value of plan assets excluding measured using NAV | 2,432 | 1,579
Pension Plan [Member] | UNITED STATES | Other Investments [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Other investments | 677 | 1,200
Pension Plan [Member] | UNITED STATES | Level 1 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Short-term investments | 9 | 0
Equity securities | 1,154 | 728
Derivative Instruments Fair Value |  | 3
Defined benefit plan, fair value of plan assets excluding measured using NAV | 1,609 | 937
Pension Plan [Member] | UNITED STATES | Level 2 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Short-term investments | 52 | 43
Equity securities | 0 | 0
Derivative Instruments Fair Value |  | 0
Defined benefit plan, fair value of plan assets excluding measured using NAV | 823 | 637
Pension Plan [Member] | UNITED STATES | Level 3 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Short-term investments | 0 | 0
Equity securities | 0 | 0
Derivative Instruments Fair Value |  | 0
Defined benefit plan, fair value of plan assets excluding measured using NAV | 0 | 5
Pension Plan [Member] | Non-US [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Short-term investments | 5 | 2
Equity securities | 614 | 512
Defined benefit plan, fair value of plan assets excluding measured using NAV | 1,075 | 949
Pension Plan [Member] | Non-US [Member] | Other Investments [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Other investments | 95 | 13
Pension Plan [Member] | Non-US [Member] | Level 1 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Short-term investments | 5 | 2
Equity securities | 122 | 100
Defined benefit plan, fair value of plan assets excluding measured using NAV | 127 | 102
Pension Plan [Member] | Non-US [Member] | Level 2 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Short-term investments | 0 | 0
Equity securities | 492 | 412
Defined benefit plan, fair value of plan assets excluding measured using NAV | 948 | 847
Pension Plan [Member] | Non-US [Member] | Level 3 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Short-term investments | 0 | 0
Equity securities | 0 | 0
Defined benefit plan, fair value of plan assets excluding measured using NAV |  | 0
Pension Plan [Member] | US Treasury and Government [Member] | UNITED STATES |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Available for sale, Fair Value | 525 | 318
Pension Plan [Member] | US Treasury and Government [Member] | UNITED STATES | Level 1 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Available for sale, Fair Value | 446 | 206
Pension Plan [Member] | US Treasury and Government [Member] | UNITED STATES | Level 2 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Available for sale, Fair Value | 79 | 112
Pension Plan [Member] | US Treasury and Government [Member] | UNITED STATES | Level 3 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Available for sale, Fair Value | 0 | 0
Pension Plan [Member] | Foreign Government Debt Securities [Member] | UNITED STATES |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Available for sale, Fair Value | 692 | 487
Pension Plan [Member] | Foreign Government Debt Securities [Member] | UNITED STATES | Level 1 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Available for sale, Fair Value | 0 | 0
Pension Plan [Member] | Foreign Government Debt Securities [Member] | UNITED STATES | Level 2 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Available for sale, Fair Value | 692 | 482
Pension Plan [Member] | Foreign Government Debt Securities [Member] | UNITED STATES | Level 3 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Available for sale, Fair Value | 0 | 5
Pension Plan [Member] | Foreign Government Debt Securities [Member] | Non-US [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Available for sale, Fair Value | 456 | 435
Pension Plan [Member] | Foreign Government Debt Securities [Member] | Non-US [Member] | Level 1 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Available for sale, Fair Value | 0 | 0
Pension Plan [Member] | Foreign Government Debt Securities [Member] | Non-US [Member] | Level 2 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Available for sale, Fair Value | 456 | 435
Pension Plan [Member] | Foreign Government Debt Securities [Member] | Non-US [Member] | Level 3 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Available for sale, Fair Value | $ 0 | $ 0

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