Benefit Plans (Postretirement Health Care Costs) (Details) - Other Postretirement Benefit Plan, Defined Benefit [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 4	$ 3	$ 13	$ 11
Interest cost	24	26	75	80
Amortization of net loss	10	3	33	17
Amortization of prior service credit	(10)	(11)	(30)	(32)
Net Periodic Benefit Cost	$ 28	$ 21	$ 91	$ 76