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Stock-Based Compensation (Details) $ in Millions | 1 Months Ended | 12 Months Ended
--- | --- | ---
Feb. 28, 2017 shares | Dec. 31, 2012 shares | Dec. 31, 2018 USD ($) performance_criteria shares | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) shares
Stock-Based Compensation |  |  |  |  |
Compensation cost that has been charged against income | $ |  |  | $ 20 | $ 21 | $ 19
Total income tax benefit recognized | $ |  |  | 7 | 15 | 10
Total unrecognized compensation cost related to nonvested share-based compensation arrangements granted | $ |  |  | $ 9 |  |
Expected weighted-average period of recognition of unrecognized compensation cost |  |  | 2 years |  |
Total fair value of shares vested | $ |  |  | $ 24 | 22 | 22
Performance Shares |  |  |  |  |
Number of performance element criteria | performance_criteria |  |  | 2 |  |
Performance period |  |  | 3 years |  |
Restricted stock unit awards |  |  |  |  |
Stock-Based Compensation |  |  |  |  |
Share-based liabilities paid | $ |  |  | $ 4 | 4 | 3
Cash flow effect, cash used to settle awards | $ |  |  | $ 5 | $ 4 | $ 3
Restricted Stock Units, Stock Grants and Stock Units |  |  |  |  |
Vesting period |  |  | 4 years |  |
Percentage of cash that the participant may elect as a dividend for the first option available under the plan |  |  | 50.00% |  |
Percentage of stock that the participant may elect as dividend under second option of plan |  |  | 50.00% |  |
Restricted Stock Units, Stock Grants, and Stock Units |  |  |  |  |
Restricted Stock Units, Stock Grants and Stock Units |  |  |  |  |
Granted (in shares) |  |  | 132,997 |  |
Shares released during period (in shares) |  |  | 5,356 |  |
Performance Shares |  |  |  |  |
Restricted Stock Units, Stock Grants and Stock Units |  |  |  |  |
Granted (in shares) |  |  | 171,708 |  |
Shares released during period (in shares) |  |  | 9,542 |  |
Performance Shares | Maximum |  |  |  |  |
Performance Shares |  |  |  |  |
Exact number of shares issued as a percentage of the target award |  |  | 200.00% |  |
Performance Shares | Minimum |  |  |  |  |
Performance Shares |  |  |  |  |
Exact number of shares issued as a percentage of the target award |  |  | 0.00% |  |
Officers and Key Employees | Restricted stock unit awards |  |  |  |  |
Restricted Stock Units, Stock Grants and Stock Units |  |  |  |  |
Percentage of fully transferable shares of stock that the participant may elect as a deferral for the first option available under the plan |  |  | 100.00% |  |
Percentage of fully transferable shares of stock in that participant may receive cash |  |  | 100.00% |  |
Chief Executive Officer | Retention units |  |  |  |  |
Restricted Stock Units, Stock Grants and Stock Units |  |  |  |  |
Granted (in shares) |  | 50,617 |  |  |
Additional shares to be granted as retention award if performance requirements are met (in shares) |  |  |  |  | 33,745
Shares released during period (in shares) | 84,362 |  |  |  |
Non-Officer Board of Director Member | Restricted stock unit awards |  |  |  |  |
Restricted Stock Units, Stock Grants and Stock Units |  |  |  |  |
Percentage of fully transferable shares of stock that the participant may elect as a deferral for the first option available under the plan |  |  | 100.00% |  |
Percentage of cash that the participant may elect as a dividend for the first option available under the plan |  |  | 100.00% |  |
Percentage of stock that the participant may elect as dividend under second option of plan |  |  | 50.00% |  |
Percentage of cash that the participant may elect as a dividend equivalent deferral for the first option available under the plan |  |  | 50.00% |  |
Percentage of fully transferable shares of stock that the participant may elect as a dividend equivalent deferral for the first option available under the plan |  |  | 50.00% |  |
2012 Plan |  |  |  |  |
Stock-Based Compensation |  |  |  |  |
Common shares available for grant (in shares) |  |  | 4,600,000 |  |
Common shares available for issuance (in shares) |  |  | 1,900,000 |  |

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- Definition Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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