Postretirement Plans (Details) (USD $)
In Millions, unless otherwise specified
 3 Months Ended 9 Months Ended 3 Months Ended 9 Months Ended 3 Months Ended 9 Months Ended
Sep. 30, 2012
Dec. 31, 2011
Sep. 30, 2012
Pension Plans, Defined Benefit [Member]
Sep. 30, 2011
Pension Plans, Defined Benefit [Member]
Sep. 30, 2012
Pension Plans, Defined Benefit [Member]
Sep. 30, 2011
Pension Plans, Defined Benefit [Member]
Sep. 30, 2012
Other Postretirement Benefit Plans, Defined Benefit [Member]
Sep. 30, 2011
Other Postretirement Benefit Plans, Defined Benefit [Member]
Sep. 30, 2012
Other Postretirement Benefit Plans, Defined Benefit [Member]
Sep. 30, 2011
Other Postretirement Benefit Plans, Defined Benefit [Member]
Sep. 30, 2011
Other Postretirement Benefit Plans, Defined Benefit [Member]
Postretirement Plan Adjustment [Member]
Sep. 30, 2011
Other Postretirement Benefit Plans, Defined Benefit [Member]
Postretirement Plan Adjustment [Member]
Defined Benefit Plan Disclosure [Line Items]                        
Service cost     $ 411 $ 351 $ 1,233 $ 1,053 $ 36 $ 110 $ 108 $ 182 $ 73 $ 73
Interest cost     751 780 2,253 2,339 79 171 237 377 68 68
Expected return on plan assets     (958) (935) (2,874) (2,805) (2) (2) (6) (4)    
Amortization of prior service costs     56 61 168 182 (49) (24) (147) (72)    
Recognized net actuarial loss     484 314 1,452 942 30 76 90 142 (43) (43)
Settlement and curtailment loss/(gain)        9 10 64       (2)       
Net periodic benefit cost     744 580 2,242 1,775 94 331 280 625 184 184
Net periodic benefit cost included in Earnings from operations     583 389 1,831 1,304 132 281 414 561 161 161
Defined Benefit Plan, Benefit Obligation                     294 294
Portion of additional net periodic benefit cost remaining in inventory 36,817 32,240                 23 23
Contributions to postretirement benefit plans         $ 1,513 $ 500     $ 11 $ 12