Benefit Plans (Postretirement Health Care Costs) (Details) (Other Postretirement Benefit Plan, Defined Benefit [Member], USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 4	$ 4
Interest cost	26	27
Amortization of net loss	12	7
Amortization of prior service credit	(10)	(11)
Net Periodic Benefit Cost	$ 32	$ 27