Retirement Benefits and Trusteed Assets (Details 3) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012
Pension Plans, Defined Benefit [Member]
Pension Benefits to be Paid Over the Next 5 Years and Thereafter [Line Items]
Defined Benefit Plan, Expected Future Benefit Payments in 2013	$ 182
Defined Benefit Plan, Expected Future Benefit Payments in 2014	187
Defined Benefit Plan, Expected Future Benefit Payments in 2015	193
Defined Benefit Plan, Expected Future Benefit Payments in 2016	200
Defined Benefit Plan, Expected Future Benefit Payments in 2017	208
Defined Benefit Plan, Expected Future Benefit Payments in 2018-2022	1,145
Other Postretirement Benefit Plans, Defined Benefit [Member]
Pension Benefits to be Paid Over the Next 5 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 Defined Benefit Pension Plan Expected Future Payments	$ 2,115