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Restructuring - Narrative (Details) $ in Millions | 12 Months Ended
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Dec. 31, 2018 USD ($) position | Dec. 31, 2017 USD ($) position | Dec. 31, 2016 USD ($) position
Restructuring Cost and Reserve [Line Items] |  |  |
Restructuring costs | $ 658 | $ 927 | $ 1,069
Cumulative restructuring costs incurred to date since program inception | $ 14,100 |  |
Number of positions elimination since inception of program | position | 45,510 |  |
Percentage estimate of cumulative pretax costs that will result in cash outlays (primarily from employee separation expense) (as percent) | 66.67% |  |
Percentage estimate of cumulative pretax costs that will be non-cash (primarily from accelerated depreciation of facilities) (as percent) | 33.33% |  |
Number of positions eliminated | position | 2,160 | 2,450 | 2,625
Asset abandonment, shut-down and other related costs |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |
Restructuring costs | $ 141 | $ 267 | $ 409
Facility Closing |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |
Pretax losses resulting from sales of facilities and related assets |  |  | $ 151

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