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Retirement Benefits Reitrement Benefits- Projected Benefit Obligations and Accumulated Benefit Obligations in Excess of Plan Assets (Details) - USD ($) $ in Millions | Dec. 31, 2018 | Dec. 31, 2017
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Projected Benefit Obligation In Excess Of Plan Assets [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Projected benefit obligation | $ 20,692 | $ 22,337
Fair value of net plan assets | 16,678 | 18,573
Accumulated Benefit Obligation In Excess Of Plan Assets [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Accumulated benefit obligation | $ 19,656 | $ 21,153

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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 Amount of projected 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 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=77993564&loc=d3e4179-114921 + Details
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