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Pension and Other Postretirement Benefits - Components of Net Periodic Benefit Cost (Detail) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Pension benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Service cost | $ 90 | $ 155 | $ 175
Interest cost | 234 | 431 | 577
Expected return on plan assets | (332) | (677) | (753)
Recognized net actuarial loss | 220 | 380 | 468
Amortization of prior service cost (benefit) | 5 | 13 | 16
Settlements | 0 | 19 | 16
Curtailments | 0 | 0 | 9
Special termination benefits | 0 | 2 | 16
Net periodic benefit cost | 217 | 323 | 524
Discontinued operations | 0 | 122 | 248
Net amount recognized in Statement of Consolidated Operations | 217 | 201 | 276
Other postretirement benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Service cost | 7 | 13 | 14
Interest cost | 30 | 63 | 92
Expected return on plan assets | 0 | 0 | 0
Recognized net actuarial loss | 5 | 24 | 17
Amortization of prior service cost (benefit) | (8) | (24) | (37)
Settlements | 0 | 0 | 0
Curtailments | 0 | 0 | (4)
Special termination benefits | 0 | 0 | 0
Net periodic benefit cost | 34 | 76 | 82
Discontinued operations | 0 | 41 | 43
Net amount recognized in Statement of Consolidated Operations | 34 | 35 | 39
Decrease in net periodic benefit cost for the recognition of the federal subsidy awarded under Medicare Part D | 11 | 22 | 34
United States | Pension benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net periodic benefit cost | $ 206 | $ 261 | $ 423

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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/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(4) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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