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Shareholders' Equity - Schedule of Stock Repurchases (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions | 3 Months Ended | 6 Months Ended | 87 Months Ended
--- | --- | --- | ---
Jun. 30, 2019 | Mar. 31, 2019 | Jun. 30, 2018 | Mar. 31, 2018 | Jun. 30, 2019 | Jun. 30, 2018 | Jun. 30, 2019
Class of Stock [Line Items] |  |  |  |  |  |  |
Shares purchased (in shares) |  |  |  |  |  |  | 124.6
Total repurchase cost | $ 1,056 | $ 101 | $ 402 | $ 553 |  |  | $ 12,200
2012 - Share Repurchase Program |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |
Shares purchased (in shares) | 5.8 |  | 2.8 |  | 6.4 | 6.7 |
Average price per share of stock repurchased (in dollars per share) | $ 183.23 |  | $ 141.23 |  | $ 181.07 | $ 141.06 |
Total repurchase cost | $ 1,050 |  | $ 400 |  | $ 1,150 | $ 950 |
Additional associated costs | 6 |  | 2 |  | 7 | 5 |
Total repurchase and associated costs | $ 1,056 |  | $ 402 |  | $ 1,157 | $ 955 |

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