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Pension, OPEB and Savings Plans (Reconciliations Of The Beginning And Ending Balances Of Pension And OPEB Plans' Level 3 Assets) (Details) $ in Millions | Dec. 31, 2017 USD ($)
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Defined Benefit Plan Disclosure [Line Items] |  |
Fair Value of Assets at Beginning of Year | $ 5,599 | [1]
Fair Value of Assets at End of Year | 6,310 | [1]
Pension And OPEB Plans Level 3 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Fair Value of Assets at Beginning of Year |  |
Fair Value of Assets at End of Year |  |
Private Equity [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Fair Value of Assets at Beginning of Year | 16 | [2]
Fair Value of Assets at End of Year | $ 14 | [2]
[1] | Excludes net receivable of $13 million and $14 million at December 31, 2017 and 2016, respectively, which consists of interest, dividends and receivables and payables related to pending securities sales and purchases.
[2] | Private equity investments primarily include various limited partnerships that invest in either operating companies through acquisitions or developing a portfolio of non-US distressed investments to maximize total return on capital. These investments are valued at NAV (or its equivalent) on an annual basis and have significant redemption restrictions preventing redemption until fund liquidation and limited ability to sell these investments. Fund liquidation is not expected to occur for several more years. These investments have been removed from the fair value hierarchy in accordance with the guidance on NAV practical expedient.

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