Employee Benefit Plans - Assumed Average Annual Rate of Increase in the Per Capita Cost of Covered Benefits (Detail) - Post-Employment Benefit Plan [Member]	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014
Group Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Health care cost trend rate (as a percent)	7.50%
Ultimate trend rate (as a percent)	5.00%
Year rate reaches ultimate trend rate	2024
Lifetime Prescription Cost [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Health care cost trend rate (as a percent)	9.00%
Ultimate trend rate (as a percent)	5.00%
Year rate reaches ultimate trend rate	2025
Medicare Supplement [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Health care cost trend rate (as a percent)	5.00%
Ultimate trend rate (as a percent)	5.00%
Year rate reaches ultimate trend rate	2017
Pre-Medicare [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Health care cost trend rate (as a percent)		8.00%
Ultimate trend rate (as a percent)		5.00%
Year rate reaches ultimate trend rate		2028
Post-Medicare [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Health care cost trend rate (as a percent)		7.00%
Ultimate trend rate (as a percent)		5.00%
Year rate reaches ultimate trend rate		2024

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.

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=35743120&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=35743120&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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- Definition

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.

+ References

No definition available.

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