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Significant Transactions (Unaudited Pro Forma Information) (Details) - USD ($) $ / shares in Units, $ in Millions | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017
Business Combinations [Abstract] |  |
Revenue | $ 109,518 | $ 102,971
Net income attributable to Comcast Corporation | $ 12,176 | $ 22,085
Basic earnings per common share attributable to Comcast Corporation shareholders (in dollars per share) | $ 2.66 | $ 4.69
Diluted earnings per common share attributable to Comcast Corporation shareholders (in dollars per share) | $ 2.62 | $ 4.61

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