| **Postretirement Benefits - Amounts Recognized in Balance Sheet and in Accumulated Other Comprehensive Loss (Details) (USD $)In Millions, unless otherwise specified** | 12 Months Ended |
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| **Amounts recognized in our Consolidated Balance Sheets consist of:**                                                                                                  |            |   |   |
| Noncurrent liability                                                                                                                                                   | $ 2,564         | $ 3,405 |   |
| Net liability recognized                                                                                                                                               | 2,652           | 3,511 |   |
| Pension Plan, Defined Benefit [Member]                                                                                                                                 |            |   |   |
| **Amounts recognized in our Consolidated Balance Sheets consist of:**                                                                                                  |            |   |   |
| Current liability                                                                                                                                                      | 14              | 14 |   |
| Noncurrent liability                                                                                                                                                   | 1,410           | 2,067 |   |
| Net liability recognized                                                                                                                                               | 1,424           | 2,081 |   |
| Amounts recognized in our accumulated other comprehensive loss consist of:                                                                                             | (585)           | 357 | 267 |
| Net actuarial loss                                                                                                                                                     | (1,947)         | (2,529) |   |
| Net prior service cost (benefit)                                                                                                                                       | 1               | 3 |   |
| Net amount recognized                                                                                                                                                  | 1,948           | 2,532 |   |
| Other Postretirement Benefit Plan, Defined Benefit [Member]                                                                                                            |            |   |   |
| **Amounts recognized in our Consolidated Balance Sheets consist of:**                                                                                                  |            |   |   |
| Current liability                                                                                                                                                      | 73              | 92 |   |
| Noncurrent liability                                                                                                                                                   | 1,154           | 1,337 |   |
| Net liability recognized                                                                                                                                               | 1,227           | 1,429 |   |
| Amounts recognized in our accumulated other comprehensive loss consist of:                                                                                             | (200)           | (88) | 893 |
| Net actuarial loss                                                                                                                                                     | (354)           | (558) |   |
| Net prior service cost (benefit)                                                                                                                                       | (10)            | (13) |   |
| Net amount recognized                                                                                                                                                  | $ 344           | $ 545 |   |

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| - Definition
The pretax total of net gain (loss), prior service cost (credit), and transition assets (obligations), as well as minimum pension liability if still remaining, included in accumulated other comprehensive income associated with a defined benefit pension or other postretirement plan(s) because they have yet to be recognized as components of net periodic benefit cost.
+ References
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| - Definition
The pretax net amount of gains and losses that are not yet recognized as a component of net periodic benefit cost, and that are recognized as increases or decreases in other comprehensive income as they arise. Gains and losses are due to changes in the value of either the benefit obligation or the plan assets resulting from experience different from that assumed or from a change in an actuarial assumption, or the consequence of a decision to temporarily deviate from the substantive plan.
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| - Definition
Amount related to the pretax cost of benefit changes attributable to plan participants' prior service pursuant to a plan amendment or a plan initiation, which has not yet been recognized as components of net periodic benefit cost.
+ References
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|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount before tax, after reclassification adjustments, of (increase) decrease in accumulated other comprehensive (income) loss related to pension and other postretirement defined benefit plans.
+ References
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|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
For a classified balance sheet, the amount recognized in balance sheet as a current liability associated with an underfunded defined benefit plan.
+ References
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| - Definition
This represents the entire liability recognized in the balance sheet that is associated with the defined benefit plans.
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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This represents the noncurrent liability for underfunded plans recognized in the balance sheet that is associated with the defined benefit pension plans and other postretirement defined benefit plans.
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