Benefit Plans - Assumed Health Care Cost Trend Rates (Detail)	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Rate to which the cost trend rate is assumed to decline (the ultimate trend rate)	0.00%
Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Health care cost trend rate assumed for next year	4.00%	4.00%	4.00%
Rate to which the cost trend rate is assumed to decline (the ultimate trend rate)	4.00%	4.00%	4.00%
Year that the rate reaches the ultimate trend rate	2017	2016	2015
Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Health care cost trend rate assumed for next year	7.00%	7.50%	8.00%
Rate to which the cost trend rate is assumed to decline (the ultimate trend rate)	5.00%	5.00%	5.00%
Year that the rate reaches the ultimate trend rate	2021	2021	2021

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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

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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

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- Definition

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

+ References

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