Segment Information - Segment Results and Operating Revenue (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Operating revenues by products and services
Revenue	$ 4,676	$ 5,029
Cost of services and products	1,985	2,136
Selling, general and administrative	800	756
Less: stock-based compensation	(23)	(20)
Total expense	2,762	2,872
Total adjusted EBITDA	1,914	2,157
Operating Segments
Operating revenues by products and services
Revenue	4,676	5,029
Cost of services and products	847	927
Selling, general and administrative	432	438
Less: stock-based compensation	0	0
Total expense	1,279	1,365
Total adjusted EBITDA	3,397	3,664
Operating Segments | Business
Operating revenues by products and services
Revenue	3,401	3,595
Cost of services and products	815	884
Selling, general and administrative	298	304
Less: stock-based compensation	0	0
Total expense	1,113	1,188
Total adjusted EBITDA	2,288	2,407
Operating Segments | Mass Markets
Operating revenues by products and services
Revenue	1,275	1,434
Cost of services and products	32	43
Selling, general and administrative	134	134
Less: stock-based compensation	0	0
Total expense	166	177
Total adjusted EBITDA	1,109	1,257
Segment Reconciling Items
Operating revenues by products and services
Revenue	0	0
Cost of services and products	1,138	1,209
Selling, general and administrative	368	318
Less: stock-based compensation	(23)	(20)
Total expense	1,483	1,507
Total adjusted EBITDA	$ (1,483)	$ (1,507)