Pension and Postretirement Benefit Plans - Summary of Asset Allocation Targets (Detail)	12 Months Ended
Dec. 31, 2015
Asset Category:
Asset allocation target (percent)	100.00%
Fixed maturity
Asset Category:
Asset allocation target (percent)	49.00%
Large-cap securities
Asset Category:
Asset allocation target (percent)	26.00%
Small-cap securities
Asset Category:
Asset allocation target (percent)	11.00%
International equity
Asset Category:
Asset allocation target (percent)	10.00%
Emerging market equity
Asset Category:
Asset allocation target (percent)	4.00%

Target allocation of investments of this type to total plan assets presented on a weighted average basis.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (c)(i)
-URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e2446-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(i)
-URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration