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Retirement Benefits (Schedule Of Allocation Of Plan Assets) (Details) - USD ($) $ in Millions | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
--- | --- | --- | ---
DB Pension Plans |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | $ 2,546 | $ 2,247 | $ 2,305
DB Pension Plans | Plan Assets Excluding Pooled Funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 1,293 | 1,246 |
DB Pension Plans | Plan Assets Excluding Pooled Funds | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 684 | 794 |
DB Pension Plans | Plan Assets Excluding Pooled Funds | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 609 | 452 |
DB Pension Plans | Cash and short-term investments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 44 | 242 |
DB Pension Plans | Cash and short-term investments | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 44 | 242 |
DB Pension Plans | U.S. government and agencies securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 66 | 11 |
DB Pension Plans | U.S. government and agencies securities | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 66 | 11 |
DB Pension Plans | Corporate debt |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 493 | 400 |
DB Pension Plans | Corporate debt | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 493 | 400 |
DB Pension Plans | State and municipal bonds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 17 | 6 |
DB Pension Plans | State and municipal bonds | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 17 | 6 |
DB Pension Plans | Foreign corporate bonds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 33 | 35 |
DB Pension Plans | Foreign corporate bonds | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 33 | 35 |
DB Pension Plans | Mutual funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 640 | 552 |
DB Pension Plans | Mutual funds | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 640 | 552 |
DB Pension Plans | Pooled funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 1,253 | 1,001 |
OPEB Plan |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 1,509 | 1,280 | $ 1,420
OPEB Plan | Plan Assets Excluding Pooled Funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 865 | 734 |
OPEB Plan | Plan Assets Excluding Pooled Funds | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 777 | 671 |
OPEB Plan | Plan Assets Excluding Pooled Funds | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 88 | 63 |
OPEB Plan | Cash and short-term investments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 9 | 36 |
OPEB Plan | Cash and short-term investments | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 9 | 36 |
OPEB Plan | U.S. government and agencies securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 10 | 2 |
OPEB Plan | U.S. government and agencies securities | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 10 | 2 |
OPEB Plan | Corporate debt |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 71 | 55 |
OPEB Plan | Corporate debt | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 71 | 55 |
OPEB Plan | State and municipal bonds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 2 | 1 |
OPEB Plan | State and municipal bonds | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 2 | 1 |
OPEB Plan | Foreign corporate bonds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 5 | 5 |
OPEB Plan | Foreign corporate bonds | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 5 | 5 |
OPEB Plan | Common stocks |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 55 | 41 |
OPEB Plan | Common stocks | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 55 | 41 |
OPEB Plan | Mutual funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 713 | 594 |
OPEB Plan | Mutual funds | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 713 | 594 |
OPEB Plan | Pooled funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | $ 644 | $ 546 |

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