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Summary of Significant Accounting Principles and Practices Schedule Of Change In Presentation (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2017 | Sep. 30, 2017 | Jun. 30, 2017 | Mar. 31, 2017 | Dec. 31, 2016 | Sep. 30, 2016 | Jun. 30, 2016 | Mar. 31, 2016 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Error Corrections and Prior Period Adjustments Restatement [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating income | $ 489 | $ 265 | $ (118) | $ 343 | $ 463 | $ 368 | $ 387 | $ 420 | $ 979 | $ 1,638 | $ 1,587
Other income (expense) |  |  |  |  |  |  |  |  | (39) | 36 | $ 100
Pension Plan | US And UK Pension Plans |  |  |  |  |  |  |  |  |  |  |
Error Corrections and Prior Period Adjustments Restatement [Line Items] |  |  |  |  |  |  |  |  |  |  |
Defined benefit plan, settlements, benefit obligation |  |  |  |  |  |  |  |  | 128 | 220 |
Accounting Standards Update 2017-06 | Adjustments |  |  |  |  |  |  |  |  |  |  |
Error Corrections and Prior Period Adjustments Restatement [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating income |  |  |  |  |  |  |  |  | 86 | 173 |
Other income (expense) |  |  |  |  |  |  |  |  | (86) | (173) |
Accounting Standards Update 2017-06 | Pro Forma |  |  |  |  |  |  |  |  |  |  |
Error Corrections and Prior Period Adjustments Restatement [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating income |  |  |  |  |  |  |  |  | 1,065 | 1,811 |
Other income (expense) |  |  |  |  |  |  |  |  | $ (125) | $ (137) |

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