Benefit Obligations (Schedule of Net Periodic Benefit Costs Recognized) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Actuarial (gain) loss on pension and postretirement plans	$ 87	$ 165	$ 46
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	2.80%	3.80%
Service cost	$ 9	$ 9	9
Interest cost	115	104	107
Expected return on plan assets	(185)	(210)	(198)
Amortization of prior service cost / (credit)	0	0	0
Actuarial (gain) loss on pension and postretirement plans	79	169	48
Curtailment (gain) loss	0	(1)	0
Special termination benefit	1	2	1
Total	$ 19	$ 73	(33)
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	2.90%	3.80%
Service cost	$ 0	$ 1	1
Interest cost	2	2	1
Expected return on plan assets	0	0	0
Amortization of prior service cost / (credit)	0	0	(1)
Actuarial (gain) loss on pension and postretirement plans	8	(4)	(2)
Curtailment (gain) loss	0	0	0
Special termination benefit	0	0	0
Total	$ 10	$ (1)	$ (1)