Retirement Benefits and Trusteed Assets (Details 8) (Other Postretirement Benefit Plans, Defined Benefit [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Other Postretirement Benefit Plans, Defined Benefit [Member]
Other Postretirement Costs [Line Items]
Service cost	$ 68	$ 64	$ 61
Interest cost	120	121	125
Expected return on plan assets	(92)	(94)	(74)
Net loss	80	55	54
Prior service cost	(27)	(26)	(4)
Net transition obligation	2	2	2
Net postretirement cost	$ 151	$ 122	$ 164