Employee Benefits - Net Periodic Benefit Income for Defined Benefit Pension Plans and Other Post-employment Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Compensation And Retirement Disclosure [Abstract]
Service cost	$ (2)	$ (2)
Interest cost	(27)	(35)
Expected return on plan assets	50	51
Total net periodic benefit income	$ 21	$ 14