Supplemental Financial Information (Components of Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Unrealized gains (losses) on marketable securities	$ 17		$ 3
Deferred gains (losses) on cash flow hedges	(16)		(75)
Unrecognized gains (losses) on employee benefit obligations	276		8
Cumulative translation adjustments	151		65
Accumulated other comprehensive income (loss), net of deferred taxes	428	$ 98	1
NBCUniversal Media LLC [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Unrealized gains (losses) on marketable securities	(139)		0
Deferred gains (losses) on cash flow hedges	1		(13)
Unrecognized gains (losses) on employee benefit obligations	118		3
Cumulative translation adjustments	76		105
Accumulated other comprehensive income (loss), net of deferred taxes	$ 56	$ (135)	$ 95