Schedule II Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for doubtful accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	$ 250	$ 226	$ 205
Additions Charged to Costs and Expenses	72	86	166
Deductions from Reserves	34	62	145
Balance at End of Year	288	250	226
Allowance for doubtful accounts [Member] | NBCUniversal Media LLC [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	84	69	60
Additions Charged to Costs and Expenses	23	26	27
Deductions from Reserves	19	11	18
Balance at End of Year	88	84	69
Allowance for returns and customer incentives [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	417	473	359
Additions Charged to Costs and Expenses	974	1,041	1,236
Deductions from Reserves	972	1,097	1,122
Balance at End of Year	419	417	473
Allowance for returns and customer incentives [Member] | NBCUniversal Media LLC [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	413	469	356
Additions Charged to Costs and Expenses	955	1,040	1,233
Deductions from Reserves	954	1,096	1,120
Balance at End of Year	414	413	469
Valuation allowance on deferred tax assets [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	266	342	375
Additions Charged to Costs and Expenses	111	23	4
Deductions from Reserves	0	99	37
Balance at End of Year	377	266	342
Valuation allowance on deferred tax assets [Member] | NBCUniversal Media LLC [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	72	71	87
Additions Charged to Costs and Expenses	15	23	4
Deductions from Reserves	0	22	20
Balance at End of Year	$ 87	$ 72	$ 71