Benefit Plans - Summary of the Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Net periodic pension cost:
Service cost	$ 118	$ 54
Interest cost	78	57
Estimated return on plan assets	(216)	(113)
Amortization and other	19	25
Net periodic benefit cost	$ (1)	$ 23