Incentive Program (Grant Value Of Restricted Stock Units) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Grant price, per share	$ 77.66	$ 81.89	$ 87.7
Units settled in stock	$ 620	$ 667	$ 771
Units settled in cash	61	63	69
Total value	$ 681	$ 730	$ 840

The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(1)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Value, after forfeitures, of stock or other type of equity granted of any equity-based compensation plan other than an employee stock ownership plan (ESOP).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 30
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=109243414&loc=d3e3913-113898

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 30
-Section 35
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6418191&loc=d3e15009-113911

+ Details

Name:	us-gaap_StockGrantedDuringPeriodValueSharebasedCompensation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Share based compensation arrangement by share based payment award restricted stock and units settled in stock.

+ References

No definition available.

+ Details

Name:	xom_ShareBasedCompensationArrangementByShareBasedPaymentAwardRestrictedStockAndUnitsSettledInStock
Namespace Prefix:	xom_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Share Based Compensation Arrangements By Share Based Payment Units Settled In Cash

+ References

No definition available.

+ Details

Name:	xom_ShareBasedCompensationArrangementsByShareBasedPaymentUnitsSettledInCash
Namespace Prefix:	xom_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration