Benefit Obligations (Schedule of Net Periodic Benefit Costs Recognized) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Actuarial (gain) loss on pension and postretirement plans	$ 96	$ 87	$ 165
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	2.10%	2.80%
Service cost	$ 12	$ 9	9
Interest cost	85	115	104
Expected return on plan assets	(199)	(185)	(210)
Actuarial (gain) loss on pension and postretirement plans	97	79	169
Curtailment (gain) loss	0	0	(1)
Special termination benefit	1	1	2
Total	$ (4)	$ 19	73
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	2.10%	2.90%
Service cost	$ 1	$ 0	1
Interest cost	1	2	2
Expected return on plan assets	0	0	0
Actuarial (gain) loss on pension and postretirement plans	(1)	8	(4)
Curtailment (gain) loss	(1)	0	0
Special termination benefit	0	0	0
Total	$ 0	$ 10	$ (1)