Benefit Obligations (Schedule of Net Periodic Benefit Costs Recognized) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2	$ 2	$ 4	$ 4
Interest cost	26	28	53	56
Expected return on plan assets	(49)	(44)	(98)	(88)
Amortization of prior service cost (credit), net	0	0	0	0
Special termination benefit	1	2	1	3
Total	(20)	(12)	(40)	(25)
Postretirement Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0	0
Interest cost	1	0	1	1
Expected return on plan assets	0	0	0	0
Amortization of prior service cost (credit), net	(1)	(1)	(1)	(2)
Special termination benefit	0	0	0	0
Total	$ 0	$ (1)	$ 0	$ (1)