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

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- Definition The entire disclosure for valuation and qualifying accounts and reserves. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 12 -Subsection 09 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 4 -Subparagraph (SX 210.12-09) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24092-122690 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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