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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 ($) | Jul. 31, 2017 USD ($) | Dec. 31, 2018 GBP (£) | Dec. 31, 2018 USD ($) | Dec. 31, 2017 GBP (£) | Dec. 31, 2017 USD ($) | Jun. 30, 2017 GBP (£) | Jun. 30, 2017 USD ($) | Dec. 31, 2018 GBP (£) | Dec. 31, 2018 USD ($) | Dec. 31, 2017 GBP (£) | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of the Company's projected benefit obligation |  |  |  | 90.00% |  |  |  |  |  | 90.00% |  |  |
U.S. |  |  |  |  |  |  |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Voluntary contribution | $ 100 |  |  |  |  |  |  |  |  |  |  |  |
Non-cash contributions by employer |  | $ 80 |  |  |  |  |  |  |  |  |  |  |
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 |  | $ 3,200 |  |  |  | $ 2,900 |  | $ 3,200 |
Plans with ABO in excess of the fair value of plan assets, ABO |  |  |  | 2,900 |  | 3,200 |  |  |  | 2,900 |  | 3,200 |
Plans with ABO in excess of the fair value of plan assets, fair value of plan assets |  |  |  | 1,800 |  | 2,000 |  |  |  | 1,800 |  | 2,000 |
Settlements |  |  |  |  |  |  |  |  |  | 0 |  | 0 |
Defined benefit plan, benefit obligation, period increase (decrease) |  |  |  |  |  | 325 |  |  |  |  |  |  |
Defined benefit plan, settlements, benefit obligation |  |  |  |  |  | 158 |  |  |  | 0 |  | 0 |
Settlement expense |  |  |  |  |  |  |  |  |  | 0 |  | 0 | $ 158
Benefit payments |  |  |  |  |  | 281 |  |  |  | 156 |  | 152 |
Future amortization of loss |  |  |  | 55 |  |  |  |  |  | 55 |  |  |
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 |  | 52 |  |  |  | 47 |  | 52 |
Plans with ABO in excess of the fair value of plan assets, ABO |  |  |  | 47 |  | 52 |  |  |  | 47 |  | 52 |
Plans with ABO in excess of the fair value of plan assets, fair value of plan assets |  |  |  | 30 |  | 30 |  |  |  | 30 |  | 30 |
Plans with PBO in excess of plan assets, plan assets |  |  |  | 30 |  | 30 |  |  |  | 30 |  | 30 |
Settlements |  |  |  |  |  |  |  |  | £ 139 | 176 | £ 371 | 496 |
Defined benefit plan, benefit obligation, period increase (decrease) |  |  | £ 122 | 154 | £ 325 | 434 | £ 103 | $ 141 |  |  |  |  |
Defined benefit plan, settlements, benefit obligation |  |  |  |  |  |  | 42 | 61 |  | 176 |  | 496 |
Settlement expense |  |  |  |  | £ (93) | 125 |  |  | £ (28) | 37 |  | 125 | 61
Benefit payments |  |  |  |  |  |  | £ 116 | $ 159 |  | 160 |  | 146 |
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 |  | 1,400 |
Plans with ABO in excess of the fair value of plan assets, ABO |  |  |  | 363 |  | 1,300 |  |  |  | 363 |  | 1,300 |
Plans with ABO in excess of the fair value of plan assets, fair value of plan assets |  |  |  | 271 |  | 1,200 |  |  |  | 271 |  | 1,200 |
Plans with PBO in excess of plan assets, plan assets |  |  |  | 1,100 |  | $ 1,200 |  |  |  | 1,100 |  | 1,200 |
Settlements |  |  |  |  |  |  |  |  |  | 0 |  | 0 |
Defined benefit plan, settlements, benefit obligation |  |  |  |  |  |  |  |  |  | 0 |  | 0 |
Settlement expense |  |  |  |  |  |  |  |  |  | 0 |  | 0 | $ 0
Benefit payments |  |  |  |  |  |  |  |  |  | 43 |  | $ 39 |
Foreign Plan | Pension Plan |  |  |  |  |  |  |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Future amortization of loss |  |  |  | $ 42 |  |  |  |  |  | $ 42 |  |  |

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- Definition Amount of payment to participant under defined benefit plan which decreases plan assets. For pension plan, payment includes, but is not limited to, pension benefits and death benefits. For other postretirement plan, payment includes, but is not limited to, prescription drug benefits, health care benefits, life insurance benefits, and legal, educational and advisory services. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 60 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=6414203&loc=d3e39716-114964 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b)(5) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 + Details
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