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Long-Term Debt (Debt Repayments) (Details) - USD ($) $ in Millions | 6 Months Ended
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Jun. 30, 2018 | Jun. 30, 2017
Debt Instrument [Line Items] |  |
Repurchases and repayments of debt | $ 4,347 | $ 4,967
NBCUniversal Enterprise 1.662% senior notes due 2018 [Member] | Senior Notes [Member] |  |
Debt Instrument [Line Items] |  |
Repurchases and repayments of debt | $ 1,100 |
Interest rate | 1.662% |
Senior 5.70% notes due 2018 [Member] | Senior Notes [Member] |  |
Debt Instrument [Line Items] |  |
Repurchases and repayments of debt | $ 1,000 |
Interest rate | 5.70% |
Senior 5.875% notes due 2018 [Member] | Senior Notes [Member] |  |
Debt Instrument [Line Items] |  |
Repurchases and repayments of debt | $ 900 |
Interest rate | 5.875% |
NBCUniveral Enterprise senior floating rate notes due 2018 [Member] | Senior Notes [Member] |  |
Debt Instrument [Line Items] |  |
Repurchases and repayments of debt | $ 700 |
Universal Studios Japan term loans maturing 2022 |  |
Debt Instrument [Line Items] |  |
Repurchases and repayments of debt | 318 |
Other [Member] |  |
Debt Instrument [Line Items] |  |
Repurchases and repayments of debt | $ 329 |

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