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 |