Employee Postretirement Benefits (Cash Contributions to its Pension Trusts) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013
Defined Benefit Pension [Member]
Defined Benefit Plan, Expected Future Benefit Payments in Year One	$ 369
Defined Benefit Plan, Expected Future Benefit Payments in Year Two	374
Defined Benefit Plan, Expected Future Benefit Payments in Year Three	374
Defined Benefit Plan, Expected Future Benefit Payments in Year Four	382
Defined Benefit Plan, Expected Future Benefit Payments in Year Five	386
Defined Benefit Plan, Expected Future Benefit Payments in Five Fiscal Years Thereafter	2,005
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan, Expected Future Benefit Payments in Year One	57
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	63
Defined Benefit Plan, Expected Future Benefit Payments in Five Fiscal Years Thereafter	$ 326