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Share-Based Compensation Plans - Performance Share Awards Narrative (Details) - Performance-based Awards - shares shares 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] |  |  |
PSA, vesting conditions period (in years) | 3 years |  |
Minimum |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
PSA, actual shares issued, percent | 0.00% |  |
Maximum |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
PSA, actual shares issued, percent | 200.00% |  |
Leadership Performance Plan Cycle 2017-2019 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Shares issued (in shares) | 0.6 |  |
Leadership Performance Plan Cycle 2016-2018 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Shares issued (in shares) |  | 0.7 |
Leadership Performance Plan Cycle 2015-2017 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Shares issued (in shares) |  |  | 1.0

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