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Pension and Other Postretirement Benefits - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2018 | Sep. 30, 2018 | Jun. 30, 2018 | Mar. 31, 2018 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |
Curtailments |  |  | $ 9 |  |  |  |
Pension benefits paid |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |
Service cost |  |  |  |  | $ 46 | $ 90 | $ 155
Interest cost |  |  |  |  | 219 | 234 | 431
Expected return on plan assets |  |  |  |  | (306) | (332) | (677)
Recognized net actuarial loss |  |  |  |  | 168 | 220 | 380
Amortization of prior service cost (benefit) |  |  |  |  | 3 | 5 | 13
Settlements |  |  |  |  | 96 | 0 | 19
Curtailments |  |  |  |  | 23 | 0 | 0
Special termination benefits |  |  |  |  | 0 | 0 | 2
Net periodic benefit cost |  |  |  |  | 249 | 217 | 323
Discontinued operations |  |  |  |  | 0 | 0 | 122
Net amount recognized in Statement of Consolidated Operations |  |  |  |  | 249 | 217 | 201
Pension benefits paid | United States |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |
Curtailments |  |  |  | $ 5 |  |  |
Net periodic benefit cost |  |  |  |  | 239 | 206 | 261
Other postretirement benefits |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |
Service cost |  |  |  |  | 7 | 7 | 13
Interest cost |  |  |  |  | 28 | 30 | 63
Expected return on plan assets |  |  |  |  | 0 | 0 | 0
Recognized net actuarial loss |  |  |  |  | 7 | 5 | 24
Amortization of prior service cost (benefit) |  |  |  |  | (7) | (8) | (24)
Settlements |  |  |  |  | 0 | 0 | 0
Curtailments | $ 9 | $ (28) |  |  | (28) | 0 | 0
Special termination benefits |  |  |  |  | 0 | 0 | 0
Net periodic benefit cost |  |  |  |  | 7 | 34 | 76
Discontinued operations |  |  |  |  | 0 | 0 | 41
Net amount recognized in Statement of Consolidated Operations |  |  |  |  | 7 | 34 | 35
Decrease in net periodic benefit cost for the recognition of the federal subsidy awarded under Medicare Part D |  |  |  |  | $ 10 | $ 11 | $ 22

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- Definition Amount of gain (loss) recognized in net periodic benefit (cost) credit of defined benefit plan. + 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)(4) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=112275985&loc=d3e4179-114921 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)(4) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e2709-114920 + Details
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