XML 44 R21.htm IDEA: XBRL DOCUMENT v2.4.0.6
Postretirement Benefit Plans - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
3 Months Ended 12 Months Ended
Mar. 31, 2013
Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]    
Liability related to funded defined-benefit pension plans $ 356 $ 353
Contributions to benefit plans 0  
Insurance cash value and Rabbi Trust investments supporting supplemental pension plan liability 55 54
Unqualified pension plan liability 59 59
Maximum
   
Defined Benefit Plan Disclosure [Line Items]    
Estimated contributions to benefit plans $ 20