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Employee Benefit Plans (Accumulated Benefit Obligation in Excess of Plan Assets) (Detail) - USD ($) $ in Millions | Dec. 31, 2017 | Dec. 31, 2016
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General Discussion Of Pension And Other Postretirement Benefits [Abstract] |  |
Accumulated benefit obligation | $ 7,392 | $ 5,987
Fair value of plan assets | $ 6,103 | $ 4,653

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- Definition Amount of accumulated benefit obligation for defined benefit pension plan with accumulated benefit obligation in excess of plan assets. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e2417-114920 + Details
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- Definition Fair value of plan assets for defined benefit pension plan with accumulated benefit obligation in excess of plan assets. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e2417-114920 + Details
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- References No definition available. + Details
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