Related Party Transactions (Condensed Consolidated Statement of Income) (Details) - USD ($) $ in Millions |
3 Months Ended | 12 Months Ended | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
Dec. 31, 2018 |
Sep. 30, 2018 |
Jun. 30, 2018 |
Mar. 31, 2018 |
Dec. 31, 2017 |
Sep. 30, 2017 |
Jun. 30, 2017 |
Mar. 31, 2017 |
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
|
| Related Party Transaction [Line Items] | |||||||||||
| Revenue | $ 27,846 | $ 22,135 | $ 21,735 | $ 22,791 | $ 22,075 | $ 21,081 | $ 21,286 | $ 20,587 | $ 94,507 | $ 85,029 | $ 80,736 |
| Total costs and expenses | (75,498) | (67,011) | (63,905) | ||||||||
| NBCUniversal Media LLC [Member] | |||||||||||
| Related Party Transaction [Line Items] | |||||||||||
| Revenue | 35,895 | 32,950 | 31,398 | ||||||||
| Total costs and expenses | (29,229) | (26,473) | (26,040) | ||||||||
| Comcast And Consolidated Subsidiaries [Member] | NBCUniversal Media LLC [Member] | |||||||||||
| Related Party Transaction [Line Items] | |||||||||||
| Revenue | 2,156 | 1,837 | 1,742 | ||||||||
| Total costs and expenses | (245) | (214) | (220) | ||||||||
| Interest expense and investment and other income (loss), net | $ (54) | $ (250) | $ (69) | ||||||||