Benefit Obligations (Schedule of Net Periodic Benefit Costs Recognized) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2	$ 3	$ 4	$ 5
Interest cost	29	26	58	52
Expected return on plan assets	(47)	(53)	(93)	(105)
Special termination benefit	0	1	0	1
Total	(16)	(23)	(31)	(47)
Postretirement Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0	0
Interest cost	1	1	1	1
Expected return on plan assets	0	0	0	0
Special termination benefit	0	0	0	0
Total	$ 1	$ 1	$ 1	$ 1