Pension and Other Postretirement Benefits - Assumptions Used in Determining Benefit Obligations and Net Periodic Benefit Cost Amounts (Detail)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Pension Benefits [Member]
Weighted average assumptions for benefit obligations at year end:
Discount rate	3.20%	4.10%
Salary increase	3.30%	3.90%
Weighted average assumptions for net periodic cost for the year:
Discount rate	4.10%	3.70%
Salary increase	3.90%	3.90%
Expected return on assets	6.70%	6.70%
Other Benefits [Member]
Weighted average assumptions for benefit obligations at year end:
Discount rate	3.70%	4.40%
Weighted average assumptions for net periodic cost for the year:
Discount rate	4.40%	4.30%
Assumed health care cost trend rates:
Health care cost trend rate assumed for next year	5.50%	7.30%
Rate that the cost trend rate gradually declines to	5.00%	5.00%
Year that the rate reaches the rate it is assumed to remain at	2016	2020

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

+ References

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- Definition

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

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- Definition

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

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- Definition

An assumption as to the rate of return on plan assets reflecting the average rate of earnings expected on the funds invested or to be invested to provide for the benefits included in the benefit obligation.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 30

-Glossary Expected Long-Term Rate of Return on Plan Assets

-URI http://asc.fasb.org/extlink&oid=6512013

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (k)(3)

-URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920

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- Definition

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

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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

-Section 50

-Paragraph 1

-Subparagraph (l)

-URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Health Care Cost Trend Rate

-URI http://asc.fasb.org/extlink&oid=6514820

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- Definition

The ultimate trend rate for health care costs.

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- Definition

Year the ultimate health care cost trend rate is expected to be reached, in CCYY format.

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