Recent Accounting Pronouncements (Effects of Changes in Revenue Recognition) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue	$ 21,915	$ 20,983	$ 21,165	$ 20,463	$ 21,025	$ 21,319	$ 19,269	$ 18,790	$ 84,526	$ 80,403	$ 74,510
Depreciation and amortization expense									10,267	9,558	$ 8,680
Cable Communications [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue									52,519	50,048
Operating Expenses Excluding Depreciation And Amortization									31,349	29,939
Depreciation and amortization expense									8,143	7,670
Cable Communications [Member] | Accounting Standards Update 2014-09 [Member] | Upon Adoption [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue									53,001	50,519
Operating Expenses Excluding Depreciation And Amortization									31,968	30,541
Depreciation and amortization expense									8,006	7,539
Cable Communications [Member] | Accounting Standards Update 2014-09 [Member] | Effect of Adoption [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue									482	471
Operating Expenses Excluding Depreciation And Amortization									619	602
Depreciation and amortization expense									$ (137)	$ (131)