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Employee Benefits - Pension Plans Narrative (Details) £ in Millions, $ in Millions | 1 Months Ended | 3 Months Ended | 12 Months Ended
--- | --- | --- | ---
Sep. 30, 2018 USD ($) | Dec. 31, 2018 GBP (£) | Dec. 31, 2018 USD ($) | Dec. 31, 2017 GBP (£) | Dec. 31, 2017 USD ($) | Dec. 31, 2019 GBP (£) | Dec. 31, 2019 USD ($) | Dec. 31, 2018 GBP (£) | Dec. 31, 2018 USD ($) | Dec. 31, 2017 GBP (£) | Dec. 31, 2017 USD ($)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |  |  |  |  |
Percentage of the Company's projected benefit obligation |  |  |  |  |  |  | 91.00% |  |  |  |
U.S. |  |  |  |  |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |  |  |  |  |
Voluntary contribution | $ 100 |  |  |  |  |  |  |  |  |  |
U.S. | Pension Plan |  |  |  |  |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |  |  |  |  |
Plans with PBO in excess of plan assets, PBO |  |  | $ 2,900 |  |  |  | $ 3,100 |  | $ 2,900 |  |
Plans with ABO in excess of the fair value of plan assets, ABO |  |  | 2,900 |  |  |  | 3,100 |  | 2,900 |  |
Plans with ABO in excess of the fair value of plan assets, fair value of plan assets |  |  | 1,800 |  |  |  | 2,000 |  | 1,800 |  |
Payment for settlements |  |  |  |  |  |  | 0 |  | 0 |  |
Non-cash settlement charge |  |  |  |  |  |  | 0 |  | 0 |  | $ 0
Amounts in Accumulated other comprehensive income (loss) expected to be recognized as components of net periodic benefit cost in next fiscal year |  |  |  |  |  |  | (68) |  |  |  |
Foreign Plan | Pension Plan |  |  |  |  |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |  |  |  |  |
Amounts in Accumulated other comprehensive income (loss) expected to be recognized as components of net periodic benefit cost in next fiscal year |  |  |  |  |  |  | (44) |  |  |  |
U.K. | Pension Plan |  |  |  |  |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |  |  |  |  |
Plans with PBO in excess of plan assets, PBO |  |  | 47 |  |  |  | 54 |  | 47 |  |
Plans with ABO in excess of the fair value of plan assets, ABO |  |  | 47 |  |  |  | 54 |  | 47 |  |
Plans with ABO in excess of the fair value of plan assets, fair value of plan assets |  |  | 30 |  |  |  | 34 |  | 30 |  |
Plans with PBO in excess of plan assets, plan assets |  |  | 30 |  |  |  |  |  | 30 |  |
Payment for settlements |  |  |  |  |  |  | 22 | £ 139 | 176 | £ 371 | 496
Reduction of projected benefit obligation |  | £ 122 | 154 | £ 325 | $ 434 |  |  |  |  |  |
Non-cash settlement charge |  |  |  | £ 93 | $ 125 | £ 4 | 5 | £ 28 | 37 |  | 125
Other | Pension Plan |  |  |  |  |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |  |  |  |  |
Plans with PBO in excess of plan assets, PBO |  |  | 1,200 |  |  |  | 1,400 |  | 1,200 |  |
Plans with ABO in excess of the fair value of plan assets, ABO |  |  | 363 |  |  |  | 406 |  | 363 |  |
Plans with ABO in excess of the fair value of plan assets, fair value of plan assets |  |  | 271 |  |  |  | 311 |  | 271 |  |
Plans with PBO in excess of plan assets, plan assets |  |  | $ 1,100 |  |  |  | 1,300 |  | 1,100 |  |
Payment for settlements |  |  |  |  |  |  | 0 |  | 0 |  |
Non-cash settlement charge |  |  |  |  |  |  | $ 0 |  | $ 0 |  | $ 0

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