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Employee Benefits Schedule of Fair Value, Assets (Details) - USD ($) $ in Millions | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
--- | --- | --- | ---
Defined Benefit Plan Disclosure [Line Items] |  |  |
Money Market Funds, at Carrying Value | $ 25 | $ 21 |
Investments, Fair Value Disclosure | 0 | 2 |
Equity securities: |  |  |
Domestic | 83 | 52 |
Defined Benefit Plan, Fair Value of Plan Assets |  | 559 |
Financial Instruments, Owned, at Fair Value | 25 | 23 |
Other Postretirement Benefit Plans assets: [Abstract] |  |  |
Money market funds |  | 4 |
Domestic equity securities - Other postretirement benefit plan assets at fair value |  | 3 |
International equity securities - other post retirement assets at fair value |  | 8 |
Private Equity Funds, Domestic [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Money Market Funds, at Carrying Value | 5 | 6 |
Investments, Fair Value Disclosure | 13 | 18 |
Equity Securities [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Investments, Fair Value Disclosure | 528 | 483 |
Fair Value, Inputs, Level 1 [Member] |  |  |
Equity securities: |  |  |
Domestic | 83 | 52 |
Private equity funds | 0 | 0 |
Defined Benefit Plan, Fair Value of Plan Assets | 83 | 52 |
Financial Instruments, Owned, at Fair Value | 13 | 8 |
Other Postretirement Benefit Plans assets: [Abstract] |  |  |
Money market funds | 3 | 4 |
Domestic equity securities - Other postretirement benefit plan assets at fair value | 0 | 0 |
International equity securities - other post retirement assets at fair value | 10 | 8 |
Other post retirement benefit plan assets total | 13 | 12 |
Fair Value, Inputs, Level 2 [Member] |  |  |
Equity securities: |  |  |
Domestic | 0 | 0 |
Private equity funds | 0 | 0 |
Defined Benefit Plan, Fair Value of Plan Assets | 0 | 0 |
Financial Instruments, Owned, at Fair Value | 19 | 39 |
Other Postretirement Benefit Plans assets: [Abstract] |  |  |
Money market funds | 0 | 0 |
Domestic equity securities - Other postretirement benefit plan assets at fair value | 3 | 3 |
International equity securities - other post retirement assets at fair value | 0 | 0 |
Other post retirement benefit plan assets total | 8 | 7 |
Fair Value, Inputs, Level 3 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Money Market Funds, at Carrying Value | 0 |  |
Equity securities: |  |  |
Domestic | 0 | 0 |
Private equity funds | 0 | 0 |
Defined Benefit Plan, Fair Value of Plan Assets | 0 | 0 |
Financial Instruments, Owned, at Fair Value | 0 | 2 |
Other Postretirement Benefit Plans assets: [Abstract] |  |  |
Money market funds | 0 | 0 |
Domestic equity securities - Other postretirement benefit plan assets at fair value | 0 | 0 |
International equity securities - other post retirement assets at fair value | 0 | 0 |
Other post retirement benefit plan assets total | 0 | 0 |
Pension Plan [Member] |  |  |
Equity securities: |  |  |
Defined Benefit Plan, Fair Value of Plan Assets | 629 | 559 | $ 550
Financial Instruments, Owned, at Fair Value | 546 | 507 |
Other Postretirement Benefit Plans [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Money Market Funds, at Carrying Value | 4 | 4 |
Investments, Fair Value Disclosure | 8 | 7 |
Equity securities: |  |  |
Defined Benefit Plan, Fair Value of Plan Assets | 33 | 30 | $ 30
Financial Instruments, Owned, at Fair Value | 12 | $ 11 |
Other Postretirement Benefit Plans assets: [Abstract] |  |  |
Money market funds | 3 |  |
Domestic equity securities - Other postretirement benefit plan assets at fair value | 3 |  |
International equity securities - other post retirement assets at fair value | $ 10 |  |

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- Definition Fair value of assets that have been segregated and restricted to provide pension or postretirement benefits. Assets include, but are not limited to, stocks, bonds, other investments, earnings from investments, and contributions by the employer and employees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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