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Recently Adopted and Recently Issued Accounting Guidance - Additional Information (Detail) - USD ($) $ in Millions | 6 Months Ended
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Jun. 30, 2017 | Jun. 30, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |
Non-service related net periodic pension cost | $ 150 |
Net periodic postretirement benefit cost | 108 | $ 168
Postretirement Benefit Costs [Member] |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |
Net periodic postretirement benefit cost | $ 150 |

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- Definition Amount of net periodic benefit cost (credit) for 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) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Details
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