Supplemental Financial Information (Cash, Cash Equivalents and Restricted Cash) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplemental Financial Information [Line Items]
Cash and cash equivalents	$ 3,814	$ 3,428
Restricted cash included in other current assets	46	60
Restricted cash included in other noncurrent assets, net	49	83
Cash, cash equivalents and restricted cash, end of year	3,909	3,571	$ 3,415	$ 2,423
NBCUniversal Media LLC [Member]
Supplemental Financial Information [Line Items]
Cash and cash equivalents	1,444	2,347
Restricted cash included in other noncurrent assets, net	20	30
Cash, cash equivalents and restricted cash, end of year	$ 1,464	$ 2,377	$ 1,987	$ 1,420