Segment Information - Segment Results and Operating Revenue (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Operating revenues by products and services
Revenues	$ 5,029	$ 5,228
Cost of services and products	2,136	2,235
Selling, general and administrative	756	853
Less: share-based compensation	(20)	(69)
Total expense	2,872	3,019
Total adjusted EBITDA	2,157	2,209
Operating Segments
Operating revenues by products and services
Revenues	5,029	5,228
Cost of services and products	924	956
Selling, general and administrative	439	482
Less: share-based compensation	0	0
Total expense	1,363	1,438
Total adjusted EBITDA	3,666	3,790
Operating Segments | Business
Operating revenues by products and services
Revenues	3,595	3,737
Cost of services and products	881	907
Selling, general and administrative	306	342
Less: share-based compensation	0	0
Total expense	1,187	1,249
Total adjusted EBITDA	2,408	2,488
Operating Segments | Mass Markets
Operating revenues by products and services
Revenues	1,434	1,491
Cost of services and products	43	49
Selling, general and administrative	133	140
Less: share-based compensation	0	0
Total expense	176	189
Total adjusted EBITDA	1,258	1,302
Operations and Other
Operating revenues by products and services
Revenues	0	0
Cost of services and products	1,212	1,279
Selling, general and administrative	317	371
Less: share-based compensation	(20)	(69)
Total expense	1,509	1,581
Total adjusted EBITDA	$ (1,509)	$ (1,581)