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Investments (Marketable Equity Securities) (Details) - USD ($) $ in Millions |  | 1 Months Ended | 12 Months Ended
--- | --- | --- | ---
Mar. 31, 2017 | Mar. 31, 2017 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Schedule of Marketable Equity Securities [Line Items] |  |  |  |  |
Realized and unrealized gains (losses) on equity securities, net |  |  | $ 656 | $ (187) | $ (17)
Marketable equity securities |  |  | 353 | 341 |
Nonmarketable equity securities |  |  | 1,896 | 1,805 |
NBCUniversal Media LLC [Member] |  |  |  |  |
Schedule of Marketable Equity Securities [Line Items] |  |  |  |  |
Realized and unrealized gains (losses) on equity securities, net |  |  | 466 | (217) | $ 0
Marketable equity securities |  |  | 295 | 162 |
Nonmarketable equity securities |  |  | 804 | 811 |
Snap [Member] |  |  |  |  |
Schedule of Marketable Equity Securities [Line Items] |  |  |  |  |
Payments to acquire marketable equity securities |  | $ 500 |  |  |
Marketable equity securities, recognized realized gains (losses) |  |  | 293 |  |
Marketable equity securities, recognized unrealized gains (losses) |  |  |  | (268) |
Marketable equity securities |  |  |  | 162 |
Snap [Member] | NBCUniversal Media LLC [Member] |  |  |  |  |
Schedule of Marketable Equity Securities [Line Items] |  |  |  |  |
Contributions from member | $ 662 |  |  |  |
Marketable equity securities, recognized realized gains (losses) |  |  | 293 |  |
Marketable equity securities, recognized unrealized gains (losses) |  |  |  | (268) |
Marketable equity securities |  |  |  | 162 |
Peloton [Member] |  |  |  |  |
Schedule of Marketable Equity Securities [Line Items] |  |  |  |  |
Realized and unrealized gains (losses) on equity securities, net |  |  | 184 |  |
Marketable equity securities |  |  | 294 |  |
Nonmarketable equity securities |  |  |  | 110 |
Peloton [Member] | NBCUniversal Media LLC [Member] |  |  |  |  |
Schedule of Marketable Equity Securities [Line Items] |  |  |  |  |
Realized and unrealized gains (losses) on equity securities, net |  |  | 184 |  |
Marketable equity securities |  |  | $ 294 |  |
Nonmarketable equity securities |  |  |  | $ 110 |

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