Pension and Other Postretirement Benefits - Summary of Effect of One Percent Change in Assumed Health Care Cost (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014
Compensation and Retirement Disclosure [Abstract]
Effect of one percentage point increase in total service and interest cost	$ 1
Effect of one percentage point increase in postretirement benefit obligation	18
Effect of one percentage point decrease in total service and interest cost	(1)
Effect of one percentage point decrease in postretirement benefit obligation	$ (20)

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Amount of effect of a one-percentage-point decrease in the assumed health care cost trend rates on the accumulated postretirement benefit obligation for health care benefits.

+ 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 (m)

-URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920

+ Details

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- Definition

Amount of effect of a one-percentage-point decrease in the assumed health care cost trend rates on the aggregate of the service and interest cost components of net periodic postretirement health care benefit costs.

+ References

+ Details

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- Definition

The effect of a one-percentage-point increase in the assumed health care cost trend rates on the accumulated postretirement benefit obligation for health care benefits.

+ References

+ Details

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- Definition

The effect of a one-percentage-point increase in the assumed health care cost trend rates on the aggregate of the service and interest cost components of net periodic postretirement health care benefit costs.

+ References

+ Details

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