Employee Postretirement Benefits (Cash Contributions to its Pension Trusts) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011
Defined Benefit Pension [Member]
Defined Benefit Plan, Expected Future Benefit Payments in Year One	$ 362
Defined Benefit Plan, Expected Future Benefit Payments in Year Two	356
Defined Benefit Plan, Expected Future Benefit Payments in Year Three	356
Defined Benefit Plan, Expected Future Benefit Payments in Year Four	361
Defined Benefit Plan, Expected Future Benefit Payments in Year Five	365
Defined Benefit Plan, Expected Future Benefit Payments in Five Fiscal Years Thereafter	1,957
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan, Expected Future Benefit Payments in Year One	60
Defined Benefit Plan, Expected Future Benefit Payments in Year Two	59
Defined Benefit Plan, Expected Future Benefit Payments in Year Three	60
Defined Benefit Plan, Expected Future Benefit Payments in Year Four	61
Defined Benefit Plan, Expected Future Benefit Payments in Year Five	62
Defined Benefit Plan, Expected Future Benefit Payments in Five Fiscal Years Thereafter	$ 320