Pension and Other Postretirement Benefits (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 7	$ 7
Interest cost	41	48
Expected return on plan assets	(48)	(46)
Amortization of actuarial loss (gain)	26	24
Net periodic cost	26	33
Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	0
Interest cost	3	4
Expected return on plan assets	0	0
Amortization of actuarial loss (gain)	(4)	(4)
Net periodic cost	$ 0	$ 0