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Share-Based Compensation Plans - Share-based compensation expense recognized in continuing operations (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Total share-based compensation expense | $ 312 | $ 317 | $ 338
Tax benefit | 61 | 66 | 74
Share-based compensation expense, net of tax | 251 | 251 | 264
Employee share purchase plans |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Total share-based compensation expense | 10 | 9 | 9
Restricted share units (“RSUs”) |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Total share-based compensation expense | 186 | 198 | 186
Performance share awards (“PSAs”) |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Total share-based compensation expense | $ 116 | $ 110 | $ 143

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