Employee Benefit Plans (Pension Plan and Other Postretirement Benefit Plan Obligations and Plan Assets and Includes a Statement of the Plans Funded Status) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Changes in fair value of plan assets:
Actual return on plan assets	$ 743	$ 273
Employer contributions	40	38	39
Pension Benefits
Changes in benefit obligation:
Service cost	(116)	(108)	(102)
Interest cost	(268)	(258)	(266)
Other Postretirement Benefits
Changes in benefit obligation:
Service cost	(44)	(48)	(56)
Interest cost	(79)	(94)	(101)
Changes In Benefit Obligation | Pension Benefits
Changes in benefit obligation:
Benefit obligation at beginning of year	4,981	4,490
Service cost	116	108
Interest cost	268	258
Benefits paid	(208)	(215)
Actuarial (gains) losses during the year	967	340
Plan amendments	1	0
Settlements and curtailments	0	0
Medicare Part D reimbursement	0	0
Early Retirement Reimbursement Program	0	0
Benefit obligation at end of year	6,125	4,981
Changes In Benefit Obligation | Other Postretirement Benefits
Changes in benefit obligation:
Benefit obligation at beginning of year	1,493	1,707
Service cost	44	48
Interest cost	79	94
Benefits paid	(88)	(83)
Actuarial (gains) losses during the year	191	(210)
Plan amendments	1	(70)
Settlements and curtailments	(6)	(1)
Medicare Part D reimbursement	5	5
Early Retirement Reimbursement Program	0	3
Benefit obligation at end of year	1,719	1,493
Changes In Fair Value Of Plan Assets | Pension Benefits
Changes in fair value of plan assets:
Fair value of plan assets at beginning of year	5,145	5,106
Actual return on plan assets	611	247
Employer contributions	5	7
Benefits paid	(208)	(215)
Fair value of plan assets at end of year	5,553	5,145
Funded status at end of year	(572)	164
Changes In Fair Value Of Plan Assets | Other Postretirement Benefits
Changes in fair value of plan assets:
Fair value of plan assets at beginning of year	1,042	1,031
Actual return on plan assets	132	26
Employer contributions	16	19
Benefits paid	(34)	(34)
Fair value of plan assets at end of year	1,156	1,042
Funded status at end of year	(563)	(451)
Level 1 | Pension Benefits
Changes in fair value of plan assets:
Noncurrent pension and other postretirement benefit assets	701	677
Other current liabilities	(2)	(3)
Noncurrent pension and other postretirement benefit liabilities	(1,271)	(510)
Net amount recognized	(572)	164
Level 1 | Other Postretirement Benefits
Changes in fair value of plan assets:
Noncurrent pension and other postretirement benefit assets	1	4
Other current liabilities	(4)	(3)
Noncurrent pension and other postretirement benefit liabilities	(560)	(452)
Net amount recognized	$ (563)	$ (451)
Level 2 | Pension Benefits
Changes in fair value of plan assets:
Discount rate	4.40%	5.50%
Weighted average rate of increase for compensation	4.21%	4.21%
Level 2 | Other Postretirement Benefits
Changes in fair value of plan assets:
Discount rate	4.40%	5.50%
Weighted average rate of increase for compensation	4.22%	4.22%