Pension and Other Postretirement Benefits - Schedule of Reconciliation of Activity for Investments (Detail) - Pension and Other Postretirement Benefit Plans' Assets [Member] - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Balance at beginning of year	$ 3,925	$ 3,421
Realized gains	118	180
Unrealized gains	94	146
Purchases	640	868
Sales	(481)	(768)
Issuances	0	0
Settlements	0	0
Acquisitions	12	117
Foreign currency translation impact	(140)	(39)
Transfers in and/or out of Level 3	0	0
Balance at end of year	$ 4,168	$ 3,925

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
-Paragraph 2
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Amount of issuances of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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