Share-Based Compensation (Recognized Share-Based Compensation Expense) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Recognized share-based compensation expense	$ 159	$ 131	$ 464	$ 391
NBCUniversal Media LLC [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Recognized share-based compensation expense	38	23	103	77
Restricted share units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Recognized share-based compensation expense	99	77	284	236
Restricted share units [Member] | NBCUniversal Media LLC [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Recognized share-based compensation expense	32	19	86	64
Stock options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Recognized share-based compensation expense	52	48	155	133
Stock options [Member] | NBCUniversal Media LLC [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Recognized share-based compensation expense	3	3	10	7
Employee stock purchase plans [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Recognized share-based compensation expense	8	6	25	22
Employee stock purchase plans [Member] | NBCUniversal Media LLC [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Recognized share-based compensation expense	$ 3	$ 1	$ 7	$ 6