Supplemental financial information - Accumulated other comprehensive income (loss), net of taxes (AOCI) (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total	$ 13,333	$ 9,187
AOCI
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total	(157)	(360)	$ (347)	$ (473)
Net actuarial loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total	(155)	(359)
Prior service credit
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total	0	1
Derivative instruments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total	$ (2)	$ (2)