Supplemental financial information - Accumulated other comprehensive income (loss), net of taxes (AOCI) (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total	$ 16,273	$ 16,903
AOCI
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total	(85)	(140)	$ (205)	$ (254)
Net actuarial loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total	(71)	(144)
Prior service cost (credit)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total	(16)	1
Unrealized gains on available-for-sale investments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total	1	2
Derivative instruments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total	$ 1	$ 1