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Shareholders' Equity - Schedule of Stock Repurchases (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions | 1 Months Ended | 3 Months Ended | 6 Months Ended | 72 Months Ended
--- | --- | --- | --- | ---
Jul. 31, 2017 | Jun. 30, 2018 | Jun. 30, 2017 | Jun. 30, 2018 | Jun. 30, 2017 | Mar. 31, 2018
Class of Stock [Line Items] |  |  |  |  |  |
Shares purchased (in shares) |  |  |  |  |  | 115.0
Total repurchase cost |  |  |  | $ 955 | $ 1,160 | $ 10,500
2012 - Share Repurchase Program |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |
Shares purchased (in shares) | 0.5 | 2.8 | 8.0 | 6.7 | 9.1 |
Average price per share of stock repurchased (in dollars per share) | $ 133.24 | $ 141.23 | $ 128.54 | $ 141.06 | $ 126.85 |
Total repurchase cost | $ 60 | $ 400 | $ 1,030 | $ 950 | $ 1,154 |
Additional associated costs |  | 2 | 5 | 5 | 6 |
Total repurchase and associated costs |  | $ 402 | $ 1,035 | $ 955 | $ 1,160 |

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