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Actual Investment Allocations (Detail)

12 Months Ended

Dec. 31, 2016

Dec. 31, 2015

Dec. 31, 2014

Dec. 31, 2013

Pension Plans

Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]

Actual Allocation

100.00%

100.00%

100.00%

Pension Plans | Equity Funds

Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]

Actual Allocation

46.00%

49.00%

54.00%

Pension Plans | Fixed Income Securities

Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]

Actual Allocation

37.00%

36.00%

32.00%

Pension Plans | Equity And Debt Securities

Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]

Actual Allocation

^[1]

6.00%

5.00%

5.00%

Pension Plans | Other

Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]

Actual Allocation

^[2]

0.00%

0.00%

8.00%

Other Postretirement Benefit Plans, Defined Benefit

Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]

Actual Allocation

100.00%

100.00%

100.00%

Other Postretirement Benefit Plans, Defined Benefit | Equity Funds

Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]

Actual Allocation

53.00%

56.00%

57.00%

Other Postretirement Benefit Plans, Defined Benefit | Fixed Income Securities

Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]

Actual Allocation

47.00%

44.00%

43.00%

Scenario Forecast | Pension Plans | Equity Funds

Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]

Target Allocation

47.00%

Scenario Forecast | Pension Plans | Fixed Income Securities

Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]

Target Allocation

37.00%

Scenario Forecast | Pension Plans | Equity And Debt Securities

Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]

Target Allocation

^[1]

6.00%

Scenario Forecast | Pension Plans | Other

Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]

Target Allocation

^[2]

0.00%

Scenario Forecast | Other Postretirement Benefit Plans, Defined Benefit | Equity Funds

Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]

Target Allocation

55.00%

Scenario Forecast | Other Postretirement Benefit Plans, Defined Benefit | Fixed Income Securities

Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]

Target Allocation

45.00%

Real Estate Funds | Pension Plans

Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]

Actual Allocation

11.00%

10.00%

1.00%

Real Estate Funds | Scenario Forecast | Pension Plans

Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]

Target Allocation

10.00%

[1]	Represents investments in an asset allocation fund. This fund invests in both equity and debt securities.
[2]	Represents investments being held in cash equivalents as of December 31, 2013 pending transfer into a Real Estate Fund.

X

- Definition

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

+ References

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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- Definition

Percentage of fair value of investments (categorized by debt securities, equity securities, real estate and other plan assets) to the fair value of plan assets held.

+ References

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)
-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)(1)
-URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920

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