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Benefit Plans and Other Postretirement Benefits, Fair Value of Postretirement Benefit Plan Assets (Details) - Other Postretirement Benefits Plan [Member] - USD ($) $ in Millions | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
--- | --- | --- | ---
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract] |  |  |  |  |  |
Fair value of plan assets |  | $ 417 | [1] | $ 461 | [1] | $ 442
Plan assets at net asset value | [1] | 40 |  | 0 |  |
Level 1 |  |  |  |  |  |
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract] |  |  |  |  |  |
Fair value of plan assets | [1] | 152 |  | 212 |  |
Level 2 |  |  |  |  |  |
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract] |  |  |  |  |  |
Fair value of plan assets | [1] | 225 |  | 249 |  |
Level 3 |  |  |  |  |  |
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract] |  |  |  |  |  |
Fair value of plan assets | [1] | 0 |  | 0 |  |
Debt Securities |  |  |  |  |  |
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract] |  |  |  |  |  |
Fair value of plan assets |  | 179 |  | 198 | [2] |
Plan assets at net asset value |  | 0 |  | 0 | [2] |
Debt Securities | Level 1 |  |  |  |  |  |
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract] |  |  |  |  |  |
Fair value of plan assets |  | 0 |  | 0 | [2] |
Debt Securities | Level 2 |  |  |  |  |  |
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract] |  |  |  |  |  |
Fair value of plan assets |  | 179 |  | 198 | [2] |
Debt Securities | Level 3 |  |  |  |  |  |
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract] |  |  |  |  |  |
Fair value of plan assets |  | 0 |  | 0 | [2] |
Equity Securities [Member] |  |  |  |  |  |
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract] |  |  |  |  |  |
Fair value of plan assets |  | 0 |  | 35 | [2] |
Plan assets at net asset value |  | 0 |  | 0 | [2] |
Equity Securities [Member] | Level 1 |  |  |  |  |  |
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract] |  |  |  |  |  |
Fair value of plan assets |  | 0 |  | 35 | [2] |
Equity Securities [Member] | Level 2 |  |  |  |  |  |
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract] |  |  |  |  |  |
Fair value of plan assets |  | 0 |  | 0 | [2] |
Equity Securities [Member] | Level 3 |  |  |  |  |  |
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract] |  |  |  |  |  |
Fair value of plan assets |  | 0 |  | 0 | [2] |
Cash equivalents |  |  |  |  |  |
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract] |  |  |  |  |  |
Fair value of plan assets | [1] | 19 |  | 29 |  |
Plan assets at net asset value | [1] | 0 |  | 0 |  |
Cash equivalents | Level 1 |  |  |  |  |  |
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract] |  |  |  |  |  |
Fair value of plan assets | [1] | 19 |  | 29 |  |
Cash equivalents | Level 2 |  |  |  |  |  |
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract] |  |  |  |  |  |
Fair value of plan assets | [1] | 0 |  | 0 |  |
Cash equivalents | Level 3 |  |  |  |  |  |
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract] |  |  |  |  |  |
Fair value of plan assets | [1] | 0 |  | 0 |  |
Insurance contracts |  |  |  |  |  |
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract] |  |  |  |  |  |
Fair value of plan assets | [1] | 45 |  | 50 |  |
Plan assets at net asset value | [1] | 0 |  | 0 |  |
Insurance contracts | Level 1 |  |  |  |  |  |
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract] |  |  |  |  |  |
Fair value of plan assets | [1] | 0 |  | 0 |  |
Insurance contracts | Level 2 |  |  |  |  |  |
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract] |  |  |  |  |  |
Fair value of plan assets | [1] | 45 |  | 50 |  |
Insurance contracts | Level 3 |  |  |  |  |  |
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract] |  |  |  |  |  |
Fair value of plan assets | [1] | 0 |  | 0 |  |
Commingled Funds |  |  |  |  |  |
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract] |  |  |  |  |  |
Fair value of plan assets |  | 173 |  | 148 | [2] |
Plan assets at net asset value |  | 40 |  | 0 | [2] |
Commingled Funds | Level 1 |  |  |  |  |  |
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract] |  |  |  |  |  |
Fair value of plan assets |  | 133 |  | 148 | [2] |
Commingled Funds | Level 2 |  |  |  |  |  |
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract] |  |  |  |  |  |
Fair value of plan assets |  | 0 |  | 0 | [2] |
Commingled Funds | Level 3 |  |  |  |  |  |
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract] |  |  |  |  |  |
Fair value of plan assets |  | 0 |  | 0 | [2] |
Other |  |  |  |  |  |
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract] |  |  |  |  |  |
Fair value of plan assets | [1] | 1 |  | 1 |  |
Plan assets at net asset value | [1] | 0 |  | 0 |  |
Other | Level 1 |  |  |  |  |  |
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract] |  |  |  |  |  |
Fair value of plan assets | [1] | 0 |  | 0 |  |
Other | Level 2 |  |  |  |  |  |
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract] |  |  |  |  |  |
Fair value of plan assets | [1] | 1 |  | 1 |  |
Other | Level 3 |  |  |  |  |  |
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract] |  |  |  |  |  |
Fair value of plan assets | [1] | $ 0 |  | $ 0 |  |
[1] | (a) See Note 10 for further information on fair value measurement inputs and methods.
[2] | (a) See Note 10 for further information regarding fair value measurement inputs and methods.

X
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