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Recent Accounting Pronouncements and Tax Reform (Effect of Changes in Revenue Recognition - Statement of Income) (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2018 | Jun. 30, 2017 | Jun. 30, 2018 | Jun. 30, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |
Revenue | $ 21,735 | $ 21,286 | $ 44,526 | $ 41,873
Total costs and expenses | 16,721 | 16,718 | 34,867 | 32,763
Operating income | 5,014 | 4,568 | 9,659 | 9,110
Net Income Attributable to Comcast Corporation | 3,216 | 2,521 | 6,334 | 5,094
NBCUniversal Media LLC [Member] |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |
Revenue | 8,313 | 8,318 | 17,843 | 16,171
Total costs and expenses | 6,706 | 6,764 | 14,461 | 13,106
Operating income | 1,607 | 1,554 | 3,382 | 3,065
Net Income Attributable to Comcast Corporation | $ 1,247 | 1,279 | $ 2,760 | 2,481
Previous Reported [Member] |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |
Revenue |  | 21,165 |  | 41,628
Total costs and expenses |  | 16,607 |  | 32,540
Operating income |  | 4,558 |  | 9,088
Net Income Attributable to Comcast Corporation |  | 2,513 |  | 5,079
Previous Reported [Member] | NBCUniversal Media LLC [Member] |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |
Revenue |  | 8,331 |  | 16,199
Total costs and expenses |  | 6,780 |  | 13,139
Operating income |  | 1,551 |  | 3,060
Net Income Attributable to Comcast Corporation |  | 1,276 |  | 2,476
Effects of Adoption [Member] | Accounting Standards Update 2014-09 [Member] |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |
Revenue |  | 121 |  | 245
Total costs and expenses |  | 111 |  | 223
Operating income |  | 10 |  | 22
Net Income Attributable to Comcast Corporation |  | 8 |  | 15
Effects of Adoption [Member] | Accounting Standards Update 2014-09 [Member] | NBCUniversal Media LLC [Member] |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |
Revenue |  | (13) |  | (28)
Total costs and expenses |  | (16) |  | (33)
Operating income |  | 3 |  | 5
Net Income Attributable to Comcast Corporation |  | $ 3 |  | $ 5

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