Expected Cash Flows for the Pension Benefit and Other Postretirement Benefit Plans (Detail) $ in Millions	12 Months Ended
Dec. 31, 2015 USD ($)
Pension Plan [Member]
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months	$ 191
Defined Benefit Plan, Expected Future Benefit Payments, Year Two	172
Defined Benefit Plan, Expected Future Benefit Payments, Year Three	166
Defined Benefit Plan, Expected Future Benefit Payments, Year Four	165
Defined Benefit Plan, Expected Future Benefit Payments, Year Five	167
Defined Benefit Plan, Expected Future Benefit Payments, Five Fiscal Years Thereafter	819
Pension Plan [Member] \| Plan Participants
Defined Benefit Plans, Estimated Future Employer Contributions in Next Fiscal Year	8
Other Postretirement Benefit Plan [Member]
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months	7
Defined Benefit Plan, Expected Future Benefit Payments, Year Two	7
Defined Benefit Plan, Expected Future Benefit Payments, Year Three	6
Defined Benefit Plan, Expected Future Benefit Payments, Year Four	5
Defined Benefit Plan, Expected Future Benefit Payments, Year Five	5
Defined Benefit Plan, Expected Future Benefit Payments, Five Fiscal Years Thereafter	20
Other Postretirement Benefit Plan [Member] \| Plan Participants
Defined Benefit Plans, Estimated Future Employer Contributions in Next Fiscal Year	$ 0

Amount of benefits from a defined benefit plan expected to be paid in the five fiscal years after the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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

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- Definition

Amount of benefits from a defined benefit plan expected to be paid in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

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- Definition

Amount of benefits from a defined benefit plan expected to be paid in the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

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- Definition

Amount of benefits from a defined benefit plan expected to be paid in the fourth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

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- Definition

Amount of benefits from a defined benefit plan expected to be paid in the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

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- Definition

Amount of benefits from a defined benefit plan expected to be paid in the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

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- Definition

Amount of employer's best estimate of contributions expected to be paid to the plan during the next fiscal year beginning after the date of the latest statement of financial position.

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

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