Segment Information - Segment Results and Operating Revenue (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Operating revenues by products and services
Segment revenue	$ 3,092	$ 3,268	$ 6,274	$ 6,558
Cost of services and products	1,624	1,653	3,311	3,305
Business
Operating revenues by products and services
Segment revenue	2,490	2,578	5,014	5,169
Cost of services and products	691	761	1,429	1,499
Headcount costs	294	304	580	648
Non-headcount costs	353	349	687	690
Total segment expense	1,338	1,414	2,696	2,837
Total segment adjusted EBITDA	1,152	1,164	2,318	2,332
Mass Markets
Operating revenues by products and services
Segment revenue	602	690	1,260	1,389
Cost of services and products	13	20	27	37
Headcount costs	142	155	292	322
Non-headcount costs	130	139	243	271
Total segment expense	285	314	562	630
Total segment adjusted EBITDA	$ 317	$ 376	$ 698	$ 759