Benefit Plans - Summary of the Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Net periodic pension cost:
Service cost	$ 52	$ 59	$ 161	$ 179
Interest cost	58	50	169	150
Estimated return on plan assets	(116)	(112)	(343)	(336)
Amortization and other	29	21	80	60
Net periodic benefit cost	$ 23	$ 18	$ 67	$ 53