Benefit Plans, Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension Benefits [Member]
Net Periodic Benefit Cost Components [Abstract]
Service cost	$ 3	$ 7	$ 8
Interest cost	92	117	110
Expected return on plan assets	(173)	(159)	(179)
Amortization of unrecognized net loss	48	45	42
Settlements and curtailments	10	1	9
Net periodic (benefit) cost	(20)	11	(10)
Other Postretirement Benefits [Member]
Net Periodic Benefit Cost Components [Abstract]
Service cost			1
Interest cost	2	2	2
Expected return on plan assets	(3)	(3)	(5)
Amortization of unrecognized net loss	(1)	(1)	(1)
Amortization of unrecognized prior service benefit			(2)
Settlements and curtailments	(1)
Net periodic (benefit) cost	$ (3)	$ (2)	$ (5)