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Pension and Other Postemployment Benefits (Details 3) - Pension - USD ($) $ in Millions | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
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Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Pension investments measured at fair value | $ 6,714 | $ 6,198 |
Asset Allocation | 100.00% | 100.00% |
Investments Excluding in Investments at NAV [Member] |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Pension investments measured at fair value | $ 6,657 | $ 6,165 |
Asset Allocation | 99.00% | 100.00% |
Cash and short-term securities |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Pension investments measured at fair value | $ 379 | $ 464 |
Asset Allocation | 6.00% | 8.00% |
Domestic |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Pension investments measured at fair value | $ 722 | $ 1,061 |
Asset Allocation | 11.00% | 17.00% |
International |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Pension investments measured at fair value | $ 2,083 | $ 1,691 |
Asset Allocation | 31.00% | 27.00% |
Government bonds |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Pension investments measured at fair value | $ 251 | $ 106 |
Asset Allocation | 4.00% | 2.00% |
Corporate bonds |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Pension investments measured at fair value | $ 1,237 | $ 1,245 |
Asset Allocation | 18.00% | 20.00% |
High yield debt |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Pension investments measured at fair value | $ 689 | $ 372 |
Asset Allocation | 10.00% | 6.00% |
Mortgaged-backed securities (non-government) |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Pension investments measured at fair value | $ 31 | $ 112 |
Asset Allocation | 0.00% | 2.00% |
Hedge funds |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Pension investments measured at fair value | $ 635 | $ 500 |
Asset Allocation | 10.00% | 8.00% |
Derivatives |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Pension investments measured at fair value | $ (1) | $ (1) |
Asset Allocation | 0.00% | 0.00% |
Real Estate Funds |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Pension investments measured at fair value | $ 631 | $ 615 |
Asset Allocation | 9.00% | 10.00% |
Private Equity Funds |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Alternative investments measured at fair value | $ 57 | $ 33 |
Asset Allocation | 1.00% | 0.00% |
Level 1 | Investments Excluding in Investments at NAV [Member] |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Pension investments measured at fair value | $ 1,209 | $ 1,470 |
Level 1 | Cash and short-term securities |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Pension investments measured at fair value | 0 | 0 |
Level 1 | Domestic |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Pension investments measured at fair value | 695 | 1,048 |
Level 1 | International |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Pension investments measured at fair value | 514 | 422 |
Level 1 | Government bonds |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Pension investments measured at fair value | 0 | 0 |
Level 1 | Corporate bonds |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Pension investments measured at fair value | 0 | 0 |
Level 1 | High yield debt |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Pension investments measured at fair value | 0 | 0 |
Level 1 | Mortgaged-backed securities (non-government) |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Pension investments measured at fair value | 0 | 0 |
Level 1 | Hedge funds |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Pension investments measured at fair value | 0 | 0 |
Level 1 | Derivatives |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Pension investments measured at fair value | 0 | 0 |
Level 1 | Real Estate Funds |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Pension investments measured at fair value | 0 | 0 |
Level 2 | Investments Excluding in Investments at NAV [Member] |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Pension investments measured at fair value | 4,817 | 4,080 |
Level 2 | Cash and short-term securities |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Pension investments measured at fair value | 379 | 464 |
Level 2 | Domestic |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Pension investments measured at fair value | 27 | 13 |
Level 2 | International |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Pension investments measured at fair value | 1,569 | 1,269 |
Level 2 | Government bonds |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Pension investments measured at fair value | 251 | 106 |
Level 2 | Corporate bonds |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Pension investments measured at fair value | 1,237 | 1,245 |
Level 2 | High yield debt |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Pension investments measured at fair value | 689 | 372 |
Level 2 | Mortgaged-backed securities (non-government) |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Pension investments measured at fair value | 31 | 112 |
Level 2 | Hedge funds |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Pension investments measured at fair value | 635 | 500 |
Level 2 | Derivatives |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Pension investments measured at fair value | (1) | (1) |
Level 2 | Real Estate Funds |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Pension investments measured at fair value | 0 | 0 |
Level 3 | Investments Excluding in Investments at NAV [Member] |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Pension investments measured at fair value | 631 | 615 |
Level 3 | Cash and short-term securities |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Pension investments measured at fair value | 0 | 0 |
Level 3 | Domestic |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Pension investments measured at fair value | 0 | 0 |
Level 3 | International |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Pension investments measured at fair value | 0 | 0 |
Level 3 | Government bonds |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Pension investments measured at fair value | 0 | 0 |
Level 3 | Corporate bonds |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Pension investments measured at fair value | 0 | 0 |
Level 3 | High yield debt |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Pension investments measured at fair value | 0 | 0 |
Level 3 | Mortgaged-backed securities (non-government) |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Pension investments measured at fair value | 0 | 0 |
Level 3 | Hedge funds |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Pension investments measured at fair value | 0 | 0 |
Level 3 | Derivatives |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Pension investments measured at fair value | 0 | 0 |
Level 3 | Real Estate Funds |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Pension investments measured at fair value | $ 631 | $ 615 | $ 587

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- Definition Fair value of investment in certain entities that calculate net asset value per share. Includes, but is not limited to, by unit, membership interest, or other ownership interest. Investment includes, but is not limited to, investment in certain hedge funds, venture capital funds, private equity funds, real estate partnerships or funds. Excludes measurement of net asset value as estimate of fair value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 6A -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=66048111&loc=SL6742756-110258 + Details
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