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Stock Plans and Share-Based Compensation - Pre-tax Expense and Income Tax Benefits (Details) - USD ($) $ in Millions | 3 Months Ended
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Mar. 31, 2021 | Mar. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Total Share-Based Compensation Expense | $ 32 | $ 24
Income Tax Benefit | 9 | 9
Performance Units |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Total Share-Based Compensation Expense | 18 | 9
Stock Options |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Total Share-Based Compensation Expense | 6 | 10
Restricted Stock Units and Awards |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Total Share-Based Compensation Expense | 5 | 2
Stock Awards for Directors |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Total Share-Based Compensation Expense | 2 | 2
Employee Stock Purchase Plan |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Total Share-Based Compensation Expense | $ 1 | $ 1

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