Pension and Other Postretirement Benefits (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0	$ 7
Interest cost	36	41
Expected return on plan assets	(47)	(48)
Amortization of actuarial loss (gain)	24	26
Net periodic cost	13	26
Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	1
Interest cost	2	3
Expected return on plan assets	0	0
Amortization of actuarial loss (gain)	(3)	(4)
Net periodic cost	$ (1)	$ 0