Employee Benefit Plans Employee Benefit Plans - Contributions and Benefit Payments (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012
Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Estimated Future Employer Contributions in Next Fiscal Year	$ 64
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months	100
Defined Benefit Plan, Expected Future Benefit Payments, Year Two	102
Defined Benefit Plan, Expected Future Benefit Payments, Year Three	104
Defined Benefit Plan, Expected Future Benefit Payments, Year Four	106
Defined Benefit Plan, Expected Future Benefit Payments, Year Five	103
Defined Benefit Plan, Expected Future Benefit Payments, Five Fiscal Years Thereafter	482
Other Postretirement [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Estimated Future Employer Contributions in Next Fiscal Year	13
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months	36
Defined Benefit Plan, Expected Future Benefit Payments, Year Two	37
Defined Benefit Plan, Expected Future Benefit Payments, Year Three	37
Defined Benefit Plan, Expected Future Benefit Payments, Year Four	39
Defined Benefit Plan, Expected Future Benefit Payments, Year Five	41
Defined Benefit Plan, Expected Future Benefit Payments, Five Fiscal Years Thereafter	207
Prescription Drug Subsidy Receipts, Next Twelve Months	0
Prescription Drug Subsidy Receipts, Year Two	0
Prescription Drug Subsidy Receipts, Year Three	0
Prescription Drug Subsidy Receipts, Year Four	(1)
Prescription Drug Subsidy Receipts, Year Five	(1)
Prescription Drug Subsidy Receipts, after Year Five	$ (4)