Supplemental Financial Information (Cash, Cash Equivalents and Restricted Cash) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Supplemental Financial Information [Line Items]
Cash and cash equivalents	$ 3,498	$ 3,814
Restricted cash included in other current assets	49	46
Restricted cash included in other noncurrent assets, net	50	49
Cash, cash equivalents and restricted cash, end of period	3,597	3,909	$ 6,177	$ 3,571
NBCUniversal Media LLC [Member]
Supplemental Financial Information [Line Items]
Cash and cash equivalents	1,114	1,444
Restricted cash included in other noncurrent assets, net	22	20
Cash, cash equivalents and restricted cash, end of period	$ 1,136	$ 1,464	$ 2,256	$ 2,377