Retirement Benefits and Trusteed Assets (OPEB - Postretirement Cost Inclusions) (Details) (Other Postretirement Benefit Plan, USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Other Postretirement Benefit Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 34	$ 47	$ 68
Interest cost	89	88	120
Expected return on plan assets	(122)	(110)	(92)
Amortization of Net Loss	20	64	80
Amortization of Prior Service Cost (Credit)	(144)	(131)	(25)
Net pension cost	$ (123)	$ (42)	$ 151