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Employee Benefits - Pension Plans Narrative (Details) £ in Millions, $ in Millions | 3 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Dec. 31, 2018 USD ($) | Dec. 31, 2018 GBP (£) | Dec. 31, 2020 USD ($) | Dec. 31, 2020 GBP (£) | Dec. 31, 2019 USD ($) | Dec. 31, 2019 GBP (£) | Dec. 31, 2018 USD ($) | Dec. 31, 2018 GBP (£) | Nov. 30, 2020 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. | Pension Plan |  |  |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |  |  |
Plans with PBO in excess of plan assets, PBO |  |  | $ 3,300 |  | $ 3,100 |  |  |  |
Plans with ABO in excess of the fair value of plan assets, ABO |  |  | 3,300 |  | 3,100 |  |  |  |
Plans with ABO in excess of the fair value of plan assets, fair value of plan assets |  |  | 2,200 |  | 2,000 |  |  |  |
Payment for settlements |  |  | 0 |  | 0 |  |  |  |
Non-cash settlement charge |  |  | 0 |  | 0 |  | $ 0 |  |
U.K. | Pension Plan |  |  |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |  |  |
Estimated retirement benefits covered by insurance contract, impact amount |  |  |  |  |  |  |  |  | $ 94
Plans with PBO in excess of plan assets, PBO |  |  | 54 |  | 54 |  |  |  |
Plans with ABO in excess of the fair value of plan assets, ABO |  |  | 54 |  | 54 |  |  |  |
Plans with ABO in excess of the fair value of plan assets, fair value of plan assets |  |  | 32 |  |  |  |  |  |
Plans with PBO in excess of plan assets, plan assets |  |  |  |  | 34 |  |  |  |
Payment for settlements |  |  | 7 |  | 22 |  | 176 | £ 139 |
Reduction of projected benefit obligation | $ 154 | £ 122 |  |  |  |  |  |  |
Non-cash settlement charge |  |  | 2 | £ 2 | 5 | £ 4 | 37 | £ 28 |
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 |  |  | 1,600 |  | 1,400 |  |  |  |
Plans with ABO in excess of the fair value of plan assets, ABO |  |  | 443 |  | 406 |  |  |  |
Plans with ABO in excess of the fair value of plan assets, fair value of plan assets |  |  | 342 |  | 311 |  |  |  |
Plans with PBO in excess of plan assets, plan assets |  |  | 1,400 |  | 1,300 |  |  |  |
Payment for settlements |  |  | 0 |  | 0 |  |  |  |
Non-cash settlement charge |  |  | $ 0 |  | $ 0 |  | $ 0 |  |

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- Definition Amount of future annual benefit for defined benefit plan participant covered by insurance contract. Includes, but is not limited to, contract issued by employer or its related party. + References Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (n) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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- Definition Amount of gain (loss) recognized in net periodic benefit (cost) credit from irrevocable action relieving primary responsibility for benefit obligation and eliminating risk related to obligation and assets used to effect settlement. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(7) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 45 -Paragraph 3A -URI http://asc.fasb.org/extlink&oid=109237824&loc=SL108413299-114919 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 6 -Subparagraph (a)(7) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e2709-114920 + Details
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