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Fair Value Measurements - Schedule of Pension Plan Assets at Fair Value by Level (Details) - USD ($) $ in Millions | Dec. 31, 2018 | Dec. 31, 2017
--- | --- | ---
Defined Benefit Plan Disclosure [Line Items] |  |
Pension plan assets at fair value | $ 2,431 | $ 2,833
Total investments in the fair value hierarchy | 1,461 | 1,764
Common Stock |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Pension plan assets at fair value | 750 | 1,022
Mutual funds |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Pension plan assets at fair value | 7 | 14
Cash equivalents |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Pension plan assets at fair value | 3 | 2
Corporate bonds |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Pension plan assets at fair value | 537 | 537
Government Securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Pension plan assets at fair value | 149 | 169
Asset-backed securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Pension plan assets at fair value | 10 | 9
Derivatives and other |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Pension plan assets at fair value | 5 | 11
Level 1 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Pension plan assets at fair value | 760 | 1,038
Total investments in the fair value hierarchy | 760 | 1,038
Level 1 | Common Stock |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Pension plan assets at fair value | 750 | 1,022
Level 1 | Mutual funds |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Pension plan assets at fair value | 7 | 14
Level 1 | Cash equivalents |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Pension plan assets at fair value | 3 | 2
Level 1 | Corporate bonds |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Pension plan assets at fair value | 0 | 0
Level 1 | Government Securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Pension plan assets at fair value | 0 | 0
Level 1 | Asset-backed securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Pension plan assets at fair value | 0 | 0
Level 1 | Derivatives and other |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Pension plan assets at fair value | 0 | 0
Level 2 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Pension plan assets at fair value | 701 | 726
Total investments in the fair value hierarchy | 701 | 726
Level 2 | Common Stock |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Pension plan assets at fair value | 0 | 0
Level 2 | Mutual funds |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Pension plan assets at fair value | 0 | 0
Level 2 | Cash equivalents |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Pension plan assets at fair value | 0 | 0
Level 2 | Corporate bonds |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Pension plan assets at fair value | 537 | 537
Level 2 | Government Securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Pension plan assets at fair value | 149 | 169
Level 2 | Asset-backed securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Pension plan assets at fair value | 10 | 9
Level 2 | Derivatives and other |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Pension plan assets at fair value | 5 | 11
Investments measured at net asset value (a) |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Investments measured at net asset value | $ 970 | $ 1,069

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- Definition Assets, usually stocks, bonds, and other investments, that have been segregated and restricted (usually in a trust) to provide benefits, at their fair value as of the measurement date. Plan assets include amounts contributed by the employer (and by employees for a contributory plan) and amounts earned from investing the contributions, less benefits paid. If a plan has liabilities other than for benefits, those non-benefit obligations may be considered as reductions of plan assets. These assets exclude those measured at net asset value. + References No definition available. + Details
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- Definition Fair value of investment other than investment in equity security, investment in debt security and equity method investment. Includes, but is not limited to, investment in certain entities that calculate net asset value per share. Example includes, but is not limited to, investment in hedge fund, venture capital fund, private equity fund, and real estate partnership or fund. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 6A -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=99377789&loc=SL6742756-110258 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 35 -Paragraph 54B -URI http://asc.fasb.org/extlink&oid=99392525&loc=SL7495116-110257 + Details
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