Employee Benefits - Information for Pension Plans with Accumulated Benefit Obligation in Excess of Plan Assets (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Retirement Benefits [Abstract]
Projected benefit obligation	$ 21,190	$ 19,510
Accumulated benefit obligation	21,134	19,461
Fair value of plan assets	$ 19,388	$ 17,757

Amount of accumulated benefit obligation for defined benefit plan with accumulated benefit obligation in excess of plan assets.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e2417-114920

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 55
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=118257860&loc=d3e4179-114921

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e2417-114920

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant