Segment Information - Segment Results and Operating Revenue (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Operating revenues by products and services
Revenue	$ 4,612	$ 4,924	$ 9,288	$ 9,953
Cost of services and products	2,058	2,115	4,043	4,251
Selling, general and administrative	815	762	1,615	1,518
Less: stock-based compensation	(25)	(42)	(48)	(62)
Total expense	2,848	2,835	5,610	5,707
Total adjusted EBITDA	1,764	2,089	3,678	4,246
Operating Segments
Operating revenues by products and services
Revenue	4,612	4,924	9,288	9,953
Cost of services and products	879	903	1,726	1,830
Selling, general and administrative	420	448	852	886
Less: stock-based compensation	0	0	0	0
Total expense	1,299	1,351	2,578	2,716
Total adjusted EBITDA	3,313	3,573	6,710	7,237
Operating Segments | Business
Operating revenues by products and services
Revenue	3,416	3,522	6,817	7,117
Cost of services and products	845	863	1,660	1,747
Selling, general and administrative	284	295	582	599
Less: stock-based compensation	0	0	0	0
Total expense	1,129	1,158	2,242	2,346
Total adjusted EBITDA	2,287	2,364	4,575	4,771
Operating Segments | Mass Markets
Operating revenues by products and services
Revenue	1,196	1,402	2,471	2,836
Cost of services and products	34	40	66	83
Selling, general and administrative	136	153	270	287
Less: stock-based compensation	0	0	0	0
Total expense	170	193	336	370
Total adjusted EBITDA	1,026	1,209	2,135	2,466
Segment Reconciling Items
Operating revenues by products and services
Revenue	0	0	0	0
Cost of services and products	1,179	1,212	2,317	2,421
Selling, general and administrative	395	314	763	632
Less: stock-based compensation	(25)	(42)	(48)	(62)
Total expense	1,549	1,484	3,032	2,991
Total adjusted EBITDA	$ (1,549)	$ (1,484)	$ (3,032)	$ (2,991)