Retirement-Related Benefits - Contributions (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Jun. 30, 2021	Dec. 31, 2020
Retirement-Related Benefits
Employer contributions			$ 7	$ 3
Employer contributions, remainder of year	$ 2		2
Noncurrent liability for retirement and nonpension postretirement benefit	995		995		$ 516	$ 550
Net transfers from Parent	1,414	$ 145	2,314	$ 786
Accumulated Other Comprehensive Income (Loss)
Retirement-Related Benefits
Net transfers from Parent	$ (338)		(338)
Tax credit associated with equity transfer			128
Net Change Retirement-Related Benefit Plans
Retirement-Related Benefits
Net transfers from Parent			$ (338)