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Retirement Benefits (Summary of changes in the fair value of the plans’ Level 3 assets) (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |
Fair Value, Asset Value, Beginning | $ 323 | $ 260
Purchases | 29 | 35
Sales | (16) | (28)
Unrealized Gain/(Loss) | 2 | 68
Realized Gain/(Loss) | 0 | 1
Exchange Rate Impact | 41 | (13)
Transfers in/(out) and Other | (7) | 0
Fair Value, Asset Value, Ending | 372 | 323
Other Investments |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |
Fair Value, Asset Value, Beginning | 312 | 257
Purchases | 20 | 27
Sales | (15) | (28)
Unrealized Gain/(Loss) | (7) | 67
Realized Gain/(Loss) | 0 | 1
Exchange Rate Impact | 40 | (12)
Transfers in/(out) and Other | 0 | 0
Fair Value, Asset Value, Ending | 350 | 312
Corporate stocks |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |
Fair Value, Asset Value, Beginning | 2 | 2
Purchases | 0 | 0
Sales | 0 | 0
Unrealized Gain/(Loss) | 0 | 0
Realized Gain/(Loss) | 0 | 0
Exchange Rate Impact | 0 | 0
Transfers in/(out) and Other | 0 | 0
Fair Value, Asset Value, Ending | 2 | 2
Corporate Obligations |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |
Fair Value, Asset Value, Beginning | 9 | 1
Purchases | 9 | 8
Sales | (1) | 0
Unrealized Gain/(Loss) | 9 | 1
Realized Gain/(Loss) | 0 | 0
Exchange Rate Impact | 1 | (1)
Transfers in/(out) and Other | (7) | 0
Fair Value, Asset Value, Ending | $ 20 | $ 9

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- Definition Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Translation Adjustment + References No definition available. + Details
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- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. + References No definition available. + Details
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- Definition Amount of gain (loss) recognized in the income statement for financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 + Details
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- Definition Amount of gain (loss) recognized in other comprehensive income (loss) for financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1a) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 + Details
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- Definition Amount of purchases of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 + Details
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- Definition Amount of transfer of financial instrument classified as an asset into (out of) level 3 of the fair value hierarchy. + References No definition available. + Details
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