Segment Information - Segment Results and Operating Revenue (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Operating revenues by products and services
Segment revenue	$ 3,182	$ 3,290
Cost of services and products	1,687	1,652
Business
Operating revenues by products and services
Segment revenue	2,524	2,591
Cost of services and products	738	738
Headcount costs	286	344
Non-headcount costs	334	341
Total segment expense	1,358	1,423
Total segment adjusted EBITDA	1,166	1,168
Mass Markets
Operating revenues by products and services
Segment revenue	658	699
Cost of services and products	14	17
Headcount costs	150	167
Non-headcount costs	113	132
Total segment expense	277	316
Total segment adjusted EBITDA	$ 381	$ 383