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Capital Structure - Summary of Changes in Shares Repurchased (Details) - USD ($) $ / shares in Units, $ in Millions | 2 Months Ended | 12 Months Ended
--- | --- | ---
Feb. 27, 2020 | Apr. 30, 2019 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Capital Allocation Plan [Line Items] |  |  |  |  |
Total number of shares purchased (in shares) |  |  |  | 36,301,882 | 35,234,664
Shares repurchased under May 24, 2018 Accelerated Repurchase Agreement |  |  |  |  |
Capital Allocation Plan [Line Items] |  |  |  |  |
Total number of shares purchased (in shares) |  |  |  |  | 10,829,903
Amounts paid for shares and share equivalents purchased (in millions) |  |  |  |  | $ 354
Shares repurchased under September 5, 2018 Accelerated Repurchase Agreement |  |  |  |  |
Capital Allocation Plan [Line Items] |  |  |  |  |
Total number of shares purchased (in shares) |  |  |  |  | 13,307,130
Amounts paid for shares and share equivalents purchased (in millions) |  |  |  |  | $ 500
Other repurchases |  |  |  |  |
Capital Allocation Plan [Line Items] |  |  |  |  |
Total number of shares purchased (in shares) |  |  |  | 26,863,211 | 11,097,631
Amounts paid for shares and share equivalents purchased (in millions) |  |  |  | $ 1,008 | $ 396
Repurchases under February 28, 2019 Accelerated Share Repurchase Agreement |  |  |  |  |
Capital Allocation Plan [Line Items] |  |  |  |  |
Total number of shares purchased (in shares) |  | 9,438,671 |  |  |
Amounts paid for shares and share equivalents purchased (in millions) |  | $ 400 |  |  |
Equivalent shares purchased in lieu of tax withholding on equity compensation issuances |  |  |  |  |
Capital Allocation Plan [Line Items] |  |  |  |  |
Total number of shares purchased (in shares) |  |  |  | 936,928 |
Average price paid per share (in shares) |  |  |  | $ 38.78 |
Amounts paid for shares and share equivalents purchased (in millions) |  |  |  | $ 36 |
Capital Allocation Plan |  |  |  |  |
Capital Allocation Plan [Line Items] |  |  |  |  |
Total number of shares purchased (in shares) |  |  |  | 37,238,810 | 35,234,664
Average price paid per share (in shares) |  |  |  | $ 38.79 | $ 35.48
Amounts paid for shares and share equivalents purchased (in millions) |  |  |  | $ 1,444 | $ 1,250
Subsequent Event | Other repurchases |  |  |  |  |
Capital Allocation Plan [Line Items] |  |  |  |  |
Total number of shares purchased (in shares) | 2,428,545 |  |  |  |
Amounts paid for shares and share equivalents purchased (in millions) | $ 92 |  |  |  |
Subsequent Event | Equivalent shares purchased in lieu of tax withholding on equity compensation issuances |  |  |  |  |
Capital Allocation Plan [Line Items] |  |  |  |  |
Total number of shares purchased (in shares) | 709,536 |  |  |  |
Average price paid per share (in shares) |  |  | $ 38.24 |  |
Amounts paid for shares and share equivalents purchased (in millions) | $ 27 |  |  |  |
Subsequent Event | Capital Allocation Plan |  |  |  |  |
Capital Allocation Plan [Line Items] |  |  |  |  |
Total number of shares purchased (in shares) | 3,138,081 |  |  |  |
Average price paid per share (in shares) | $ 37.87 |  |  |  |
Amounts paid for shares and share equivalents purchased (in millions) | $ 119 |  |  |  |

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