Schedule of Assumed Health Care Cost Trend Rate (Detail)	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015
Compensation And Retirement Disclosure [Abstract]
Health care cost trend rate assumed for next year	7.00%	7.00%
Rate to which the cost trend rate gradually declines	5.00%	5.00%
Year the rate reaches the ultimate rate	2021	2020

No definition available.

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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
-Glossary Health Care Cost Trend Rate
-URI http://asc.fasb.org/extlink&oid=6514820

Reference 2: 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=65897934&loc=d3e1928-114920

+ Details

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- Definition

The ultimate trend rate for health care costs.

+ 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=65897934&loc=d3e1928-114920

+ 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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