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Shareholders' Equity - Schedule of Stock Repurchases (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions | 3 Months Ended | 4 Months Ended | 9 Months Ended | 102 Months Ended
--- | --- | --- | --- | ---
Sep. 30, 2020 | Mar. 31, 2020 | Sep. 30, 2019 | Jun. 30, 2019 | Mar. 31, 2019 | Oct. 25, 2019 | Sep. 30, 2020 | Sep. 30, 2019 | Sep. 30, 2020
Equity, Class of Treasury Stock [Line Items] |  |  |  |  |  |  |  |  |
Total repurchase cost | $ 500.0 | $ 463.0 | $ 350.0 | $ 1,056.0 | $ 101.0 |  |  |  |
2012 - Share Repurchase Program |  |  |  |  |  |  |  |  |
Equity, Class of Treasury Stock [Line Items] |  |  |  |  |  |  |  |  |
Shares purchased (in shares) | 2,400 |  | 1,800 |  |  | 25 | 4,600 | 8,200 | 133,400
Average price per share (in dollars per share) | $ 201.96 |  | $ 190.83 |  |  | $ 193.91 | $ 207.01 | $ 183.26 |
Total repurchase cost | $ 500.0 |  | $ 350.0 |  |  | $ 4.8 | $ 961.0 | $ 1,500.0 | $ 13,900.0
Additional associated costs | 0.0 |  | 0.0 |  |  |  | 2.0 | 7.0 |
Total costs recorded to retained earnings | $ 500.0 |  | $ 350.0 |  |  |  | $ 963.0 | $ 1,507.0 |

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