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Pension and Postretirement Benefit Plans - Pension Asset Fair Value Level 3 (Details) - Qualified and Non-qualified Pension Benefits - International Qualified and Non-qualified Pension Benefits - Funded - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016
Benefit Plan Information |  |
Foreign currency exchange | $ (560) | $ 444
Level 3 |  |
Benefit Plan Information |  |
Foreign currency exchange | 16 | (9)
Defined benefit plan increases related to net purchases and unrealized gains losses | $ 48 | $ 8

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- Definition Amount of foreign currency translation gain (loss) which increases (decreases) plan assets 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 (b)(2) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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