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Stockholders' Equity - Schedule of Share Repurchases (Details) - USD ($) $ / shares in Units, shares in Millions | 12 Months Ended |  |  |
--- | --- | --- | --- | ---
Mar. 31, 2018 | Mar. 31, 2017 | Mar. 31, 2016 | Oct. 31, 2016 | Oct. 31, 2015 | May 31, 2015
Stockholders' Equity Note [Abstract] |  |  |  |  |  |
Total Number of Shares Purchased (in shares) | 10.5 | 15.5 | 8.7 |  |  |
Average price paid per share (in dollars per share) | $ 151.06 | $ 141.16 | $ 173.64 |  |  |
Approximate Dollar Value of Shares that May Yet Be Purchased Under the Programs |  |  |  |  |  |
Beginning balance | $ 2,746,000,000 | $ 996,000,000 | $ 0 |  |  |
Shares repurchase plans authorized |  |  |  | $ 4,000,000,000.0 | $ 2,000,000,000 | $ 500,000,000
Shares repurchased | (1,650,000,000) | (2,250,000,000) | (1,504,000,000) |  |  |
Ending balance | $ 1,096,000,000 | $ 2,746,000,000 | $ 996,000,000 |  |  |

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- Definition Total cost of shares repurchased divided by the total number of shares repurchased. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 30 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6405813&loc=d3e23239-112655 + Details
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- Definition Number of shares that have been repurchased during the period and are being held in treasury. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(29)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21463-112644 + Details
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