Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Pension Benefits [Member]
Components of Net Periodic Benefit [Abstract]
Service cost	$ 1	$ 1
Interest cost	18	23
Expected return on plan assets	(43)	(43)
Amortization of unrecognized net loss	12	11
Settlement charge		4
Net periodic benefit	(12)	(4)
Other Postretirement Benefits [Member]
Components of Net Periodic Benefit [Abstract]
Expected return on plan assets	(1)	(1)
Net periodic benefit	$ (1)	$ (1)