Pension and Other Employee Benefits (Schedule of Reconciliation of Amounts on our Balance Sheets) (Details) - USD ($) $ in Millions |
Dec. 31, 2018 |
Dec. 31, 2017 |
|---|---|---|
| Pension Plan [Member] | ||
| Defined Benefit Plans and PRB Plans [Line Items] | ||
| Prior service (cost) credit | $ (27) | $ (22) |
| Net loss | (10,590) | (11,607) |
| Accumulated other comprehensive loss | (10,617) | (11,629) |
| Accumulated contributions in excess (below) net periodic benefit or cost | 4,482 | 4,062 |
| Net amount recognized on our balance sheets | (6,135) | (7,567) |
| PRB [Member] | ||
| Defined Benefit Plans and PRB Plans [Line Items] | ||
| Prior service (cost) credit | 0 | 0 |
| Net loss | (121) | (137) |
| Accumulated other comprehensive loss | (121) | (137) |
| Accumulated contributions in excess (below) net periodic benefit or cost | (251) | (250) |
| Net amount recognized on our balance sheets | $ (372) | $ (387) |