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Restructuring - Narrative (Details) - 2017 Plan $ in Millions | 3 Months Ended | 9 Months Ended | 21 Months Ended
--- | --- | --- | ---
Sep. 30, 2018 USD ($) | Sep. 30, 2018 USD ($) job_elimination | Sep. 30, 2018 USD ($) job_elimination
Restructuring Cost and Reserve [Line Items] |  |  |
Expected total cost | $ 1,025 | $ 1,025 | $ 1,025
Number of positions eliminated to date | job_elimination |  |  | 3,798
Costs incurred | 97 | 366 | $ 863
Workforce reduction |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |
Expected total cost | 420 | 420 | 420
Costs incurred | 18 | 84 | 383
Technology rationalization |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |
Expected total cost | 130 | 130 | 130
Costs incurred | 12 | 30 | 63
Lease consolidation |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |
Expected total cost | 60 | 60 | 60
Costs incurred | 11 | 24 | 32
Asset impairments |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |
Expected total cost | 40 | 40 | 40
Costs incurred | 2 | 11 | 37
Other Restructuring |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |
Expected total cost | 375 | 375 | 375
Costs incurred | $ 54 | $ 217 | $ 348
Minimum |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |
Expected number of positions eliminated | job_elimination |  | 4,200 |
Maximum |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |
Expected number of positions eliminated | job_elimination |  | 4,800 |

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