Employee Benefits - Weighted Average Assumptions to Determine Projected Benefit Obligations (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011
Effect on accumulated postretirement benefit obligation
One percent increase	$ 5	$ 8
One percent decrease	$ (5)	$ (8)
Pension Plans [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Discount rate	4.10%	5.10%
Rate of compensation increase	4.10%	4.10%
Postretirement Welfare Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Discount rate	3.10%	4.30%
Rate of compensation increase
Prior to age 65 [Member]
Health care cost trend rate for the next year
Health care cost trend rate assumed for next fiscal year	8.00%	8.00%
After age 65 [Member]
Health care cost trend rate for the next year
Health care cost trend rate assumed for next fiscal year	8.00%	12.00%

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- Definition

The interest rate used to adjust for the time value of money for the plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

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- Definition

Expected rate of compensation increases (for pay-related plans).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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-SubTopic 20

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- Definition

Amount of effect of a one-percentage-point decrease in the assumed health care cost trend rates on the accumulated postretirement benefit obligation for health care benefits.

+ References

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- Definition

The effect of a one-percentage-point increase in the assumed health care cost trend rates on the accumulated postretirement benefit obligation for health care benefits.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

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- Definition

The assumed health care cost trend rate for the next year used to measure the expected cost of benefits covered by the plan (gross eligible charges). This is based upon the annual rate of change in the cost of health care benefits currently provided by the postretirement benefit plan, due to factors other than changes in the composition of the plan population by age and dependency status.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Health Care Cost Trend Rate

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