Employee Postretirement Benefits (Cash Contributions to its Pension Trusts) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012
Defined Benefit Pension [Member]
Defined Benefit Plan, Expected Future Benefit Payments in Year One	$ 352
Defined Benefit Plan, Expected Future Benefit Payments in Year Two	354
Defined Benefit Plan, Expected Future Benefit Payments in Year Three	357
Defined Benefit Plan, Expected Future Benefit Payments in Year Four	357
Defined Benefit Plan, Expected Future Benefit Payments in Year Five	365
Defined Benefit Plan, Expected Future Benefit Payments in Five Fiscal Years Thereafter	1,915
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan, Expected Future Benefit Payments in Year One	58
Defined Benefit Plan, Expected Future Benefit Payments in Year Two	57
Defined Benefit Plan, Expected Future Benefit Payments in Year Three	56
Defined Benefit Plan, Expected Future Benefit Payments in Year Four	57
Defined Benefit Plan, Expected Future Benefit Payments in Year Five	58
Defined Benefit Plan, Expected Future Benefit Payments in Five Fiscal Years Thereafter	$ 300