Benefit Obligations (Schedule of Net Periodic Benefit Costs Recognized) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 3	$ 2	$ 5	$ 4
Interest cost	26	26	52	53
Expected return on plan assets	(53)	(49)	(105)	(98)
Amortization of prior service cost (credit), net	0	0	0	0
Special termination benefit	1	1	1	1
Total	(23)	(20)	(47)	(40)
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
Amortization of prior service cost (credit), net	0	(1)	0	(1)
Special termination benefit	0	0	0	0
Total	$ 1	$ 0	$ 1	$ 0