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Schedule II Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Allowance for doubtful accounts [Member] |  |  |
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |
Balance at Beginning of Year | $ 352 | $ 288 | $ 250
Additions Charged to Costs and Expenses | 769 | 616 | 554
Deductions from Reserves | 702 | 552 | 516
Balance at End of Year | 419 | 352 | 288
Allowance for doubtful accounts [Member] | NBCUniversal Media LLC [Member] |  |  |
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |
Balance at Beginning of Year | 99 | 88 | 84
Additions Charged to Costs and Expenses | 48 | 32 | 23
Deductions from Reserves | 47 | 21 | 19
Balance at End of Year | 100 | 99 | 88
Valuation allowance on deferred tax assets [Member] |  |  |
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |
Balance at Beginning of Year | 632 | 377 | 266
Additions Charged to Costs and Expenses | 1,403 | 367 | 111
Deductions from Reserves | 129 | 112 | 0
Balance at End of Year | 1,906 | 632 | 377
Valuation allowance on deferred tax assets [Member] | NBCUniversal Media LLC [Member] |  |  |
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |
Balance at Beginning of Year | 73 | 87 | 72
Additions Charged to Costs and Expenses | 36 | 13 | 15
Deductions from Reserves | 15 | 27 | 0
Balance at End of Year | $ 94 | $ 73 | $ 87

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