Benefit Plans - Summary of the Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Net periodic pension cost:
Service cost	$ 118	$ 55	$ 236	$ 109
Interest cost	78	54	156	111
Estimated return on plan assets	(217)	(114)	(433)	(227)
Amortization and other	19	26	38	51
Net periodic (benefit) cost	$ (2)	$ 21	$ (3)	$ 44