Benefit Obligations (Schedule of Net Periodic Benefit Costs Recognized) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2	$ 2	$ 7	$ 6
Interest cost	26	27	78	80
Expected return on plan assets	(52)	(50)	(157)	(148)
Amortization of prior service cost (credit), net	0	0	0	0
Special termination benefit	0	0	1	1
Total	(24)	(21)	(71)	(61)
Postretirement Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	1	0	1
Interest cost	1	0	2	1
Expected return on plan assets	0	0	0	0
Amortization of prior service cost (credit), net	0	0	0	(1)
Special termination benefit	0	0	0	0
Total	$ 1	$ 1	$ 2	$ 1