Pension and Other Postretirement Benefits - Weighted Average Assumptions Used to Determine Benefit Obligations (Detail)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Pension Benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Discount rate	4.20%	5.05%
Rate of compensation increase	5.00%	5.00%
Other Postretirement Benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Discount rate	4.15%	5.00%
Rate of compensation increase	5.00%	5.00%
Rate to which the cost trend rate is assumed to decline for all eligible retirees (the ultimate trend rate)	5.00%	5.00%
Year that the cost trend rate reaches the ultimate trend rate	2020	2020
Other Postretirement Benefits [Member] \| Pre 65 [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Health care cost trend rate assumed for current year	6.67%	7.00%
Other Postretirement Benefits [Member] \| Post 65 [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Health care cost trend rate assumed for current year	5.50%	5.60%

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

+ References

+ Details

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- Definition

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

+ References

+ Details

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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

+ Details

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- Definition

The ultimate trend rate for health care costs.

+ References

+ Details

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- Definition

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

+ References

+ Details

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- Details

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