v3.10.0.1
Schedule II Valuation and Qualifying Accounts (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Allowance for doubtful accounts [Member]      
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]      
Balance at Beginning of Year $ 288 $ 250 $ 226
Additions Charged to Costs and Expenses 616 554 558
Deductions from Reserves 552 516 534
Balance at End of Year 352 288 250
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 88 84 69
Additions Charged to Costs and Expenses 32 23 26
Deductions from Reserves 21 19 11
Balance at End of Year 99 88 84
Valuation allowance on deferred tax assets [Member]      
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]      
Balance at Beginning of Year 377 266 342
Additions Charged to Costs and Expenses 367 111 23
Deductions from Reserves 112 0 99
Balance at End of Year 632 377 266
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 87 72 71
Additions Charged to Costs and Expenses 13 15 23
Deductions from Reserves 27 0 22
Balance at End of Year $ 73 $ 87 $ 72