| **Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Millions** | Total    | Common Stock | Additional Paid-in Capital | Retained Earnings | Accumulated Other Comprehensive (Loss) | Treasury Stock |
|---------------------------------------------------------------------------------------------------|----------|--------------|----------------------------|-------------------|----------------------------------------|----------------|
| **Increase (Decrease) in Stockholders' Equity [Roll Forward]**                                    |     |         |                       |              |                                   |           |
| Cumulative effect adjustments from changes in accounting guidance, net of tax                     |     |         |                       | $ 0               | $ 0                                    |           |
| Total stockholder's equity at beginning of period (Previously reported) at Dec. 31, 2016          |     |         |                       | 9,359             | (173)                                  |           |
| Total stockholder's equity at beginning of period at Dec. 31, 2016                                |     | $ 683        | $ 2,173                    | 9,359             | (173)                                  | $ (73)         |
| **Increase (Decrease) in Stockholders' Equity [Roll Forward]**                                    |     |         |                       |              |                                   |           |
| Stock-based compensation                                                                          |     |         | (12)                       |              |                                   | 8              |
| Dividends paid to common stockholders                                                             |     |         |                       | (613)             |                                   |           |
| Net income                                                                                        | $ 260    |         |                       | 260               |                                   |           |
| Other comprehensive (loss) income                                                                 | 81       |         |                       |              | 81                                     |           |
| Total stockholder's equity at end of period at Mar. 31, 2017                                      | 11,693   | 683          | 2,161                      | 9,006             | (92)                                   | (65)           |
| **Increase (Decrease) in Stockholders' Equity [Roll Forward]**                                    |     |         |                       |              |                                   |           |
| Cumulative effect adjustments from changes in accounting guidance, net of tax                     |     |         |                       | (50)              | (16)                                   |           |
| Total stockholder's equity at beginning of period (Previously reported) at Dec. 31, 2017          |     |         |                       | 9,414             | 32                                     |           |
| Total stockholder's equity at beginning of period at Dec. 31, 2017                                | 12,244   | 683          | 2,175                      | 9,364             | 16                                     | (60)           |
| **Increase (Decrease) in Stockholders' Equity [Roll Forward]**                                    |     |         |                       |              |                                   |           |
| Stock-based compensation                                                                          |     |         | (2)                        |              |                                   | 1              |
| Dividends paid to common stockholders                                                             |     |         |                       | (627)             |                                   |           |
| Net income                                                                                        | 291      |         |                       | 291               |                                   |           |
| Other comprehensive (loss) income                                                                 | (416)    |         |                       |              | (416)                                  |           |
| Total stockholder's equity at end of period at Mar. 31, 2018                                      | $ 11,425 | $ 683        | $ 2,173                    | $ 9,028           | $ (400)                                | $ (59)         |

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|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of increase to additional paid-in capital (APIC) from recognition of equity-based compensation.
+ References
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| - Definition
Amount after tax of increase (decrease) to equity or (increase) decrease to net assets, resulting from the cumulative effect adjustment of a new accounting principle applied in the period of adoption.
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| - Definition
Amount of paid and unpaid common stock dividends declared with the form of settlement in cash.
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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.
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| - Definition
The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.
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| - Definition
Amount after tax and reclassification adjustments of other comprehensive income (loss).
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|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.
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