Retirement Plans - Change in Benefit Obligation, Fair Value of Plan Assets, and Funded Status of Pension Plans and Postretirement Medical Plan (Parenthetical) (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Lump-sum settlement payment included in Benefit payments	$ 32	$ 57
Funded Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	2,424	2,679
Unfunded Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Actuarial gains (loss) resulted from a change	29	(10)
Accumulated benefit obligation	171	190
Change in Discount Rate
Defined Benefit Plan Disclosure [Line Items]
Actuarial gains (loss) resulted from a change	$ 235	$ (170)

Amount of actuarial present value of benefits attributed to employee service rendered, excluding assumptions about future compensation level.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920

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- Definition

Amount of gain (loss) from change in actuarial assumptions which (increases) decreases benefit obligation of defined benefit plan. Assumptions include, but are not limited to, interest, mortality, employee turnover, salary, and temporary deviation from substantive plan.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)(4)
-URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920

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+ References

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Amount of (increase) decrease to benefit obligation of defined benefit plan from irrevocable action relieving primary responsibility for benefit obligation and eliminating risk for obligation and assets used to effect settlement. Includes, but is not limited to, lump-sum cash payment to participant in exchange for right to receive specified benefits, purchase of nonparticipating annuity contract and change from remeasurement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)(10)
-URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920

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