Pension and Other Postretirement Benefits (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Pension
Components of net periodic benefit cost:
Service cost	$ 14	$ 13
Interest cost	15	20
Expected return on plan assets	(28)	(30)
Amortization of actuarial loss (gain)	12	5
Total net periodic benefit cost	13	8
Other Postretirement Benefits
Components of net periodic benefit cost:
Service cost	2	2
Interest cost	4	5
Expected return on plan assets	(6)	(6)
Amortization of actuarial loss (gain)	0	0
Total net periodic benefit cost	$ 0	$ 1