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Stock-Based Compensation (Narrative) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Stock-based compensation expense on restricted stock | $ 29 | $ 24 | $ 18
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value | 11 | 1 | 21
Share-based Payment Arrangement, Exercise of Option, Tax Benefit | $ 2 | 0 | 4
Stock Options [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Stock option awards, term (in years) | 10 years |  |
Unrecognized compensation expense | $ 7 |  |
Unrecognized compensation expense, weighted-average period of recognition (in years) | 1 year 9 months 18 days |  |
Restricted Stock Units (RSUs) [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Unrecognized compensation expense | $ 18 |  |
Unrecognized compensation expense, weighted-average period of recognition (in years) | 1 year 10 months 24 days |  |
Total fair value of shares of restricted stock that vested | $ 12 | $ 28 | $ 10
Cliff Vest [Member] | Stock Options [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Stock-based compensation, vesting period | 5 years |  |
Cliff Vest [Member] | Minimum [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Stock-based compensation, vesting period | 3 years |  |
Cliff Vest [Member] | Maximum [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Stock-based compensation, vesting period | 6 years |  |
Ratably On Annual Basis [Member] | Stock Options [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Stock-based compensation, vesting period | 3 years |  |
Ratably On Annual Basis [Member] | Minimum [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Stock-based compensation, vesting period | 2 years |  |
Ratably On Annual Basis [Member] | Maximum [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Stock-based compensation, vesting period | 5 years |  |

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