Retirement Benefits and Trusteed Assets (Details 12) (Other Postretirement Benefit Plans, Defined Benefit [Member], USD $) In Millions, unless otherwise specified	Dec. 31, 2012
Other Postretirement Benefit Plans, Defined Benefit [Member]
Benefits Expected to be Paid Over the Next Five Years and Thereafter [Line Items]
Defined Benefit Plan, Expected Future Benefit Payments in 2013	$ 78
Defined Benefit Plan, Expected Future Benefit Payments in 2014	82
Defined Benefit Plan, Expected Future Benefit Payments in 2015	87
Defined Benefit Plan, Expected Future Benefit Payments in 2016	91
Defined Benefit Plan, Expected Future Benefit Payments in 2017	97
Defined Benefit Plan, Expected Future Benefit Payments in 2018-2022	556
Total Expected Future Benefit Payments	$ (2,115)