Supplemental Financial Information (Noncash Investing and Financing Activities)(Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplemental Financial Information [Line Items]
Capital expenditures incurred but not yet paid	$ 1,200	$ 1,300	$ 1,100
Dividends payable	$ 732	$ 653	$ 612
Dividends payable (in dollars per share)	$ 0.1575	$ 0.1375	$ 0.125
Capital Contribution to VIE accrued but not yet paid		$ 447
Fair value equity securities settlement			$ 517
NBCUniversal Media LLC [Member]
Supplemental Financial Information [Line Items]
Capital expenditures incurred but not yet paid	$ 325	189	287
Contribution from member	$ 662	$ 3,655	$ 252