Employee Benefit Plans (Components of Net Periodic PRB (Income) Expense) (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Aug. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Net settlement, curtailment and special termination benefits (gain) loss	$ (98)
Non-service pension benefit		$ (902)	$ (829)	$ (659)
Net periodic pension and other postretirement (income) expense		(413)	(566)	(392)
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost		6	2	2
Interest cost		37	31	26
Expected return on plan assets		(13)	(1)	0
Amortization of prior service cost (credit)		(3)	(42)	(6)
Recognized actuarial net loss		(12)	(12)	(10)
Net settlement, curtailment and special termination benefits (gain) loss		1	0	0
Non-service pension benefit		10	(24)	10
Net periodic pension and other postretirement (income) expense		$ 16	$ (22)	$ 12