Pension And Other Postretirement Benefits (Change In The Fair Value Of Level 3 Assets) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010
Pension Benefits - U.S. [Member] \| Private Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value at January 1	$ 408	$ 349
Net realized gains/(losses)	1
Net unrealized gains/(losses)	56	47
Net purchases/(sales)	(7)	12
Fair value at December 31	458	408
Pension Benefits - U.S. [Member] \| Private Mortgages [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value at January 1	128	280
Net realized gains/(losses)	5	36
Net unrealized gains/(losses)		(3)
Net purchases/(sales)	(133)	(185)
Fair value at December 31		128
Pension Benefits - Non-U.S. [Member] \| Private Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value at January 1	315	239
Net realized gains/(losses)	7	(1)
Net unrealized gains/(losses)	33	26
Net purchases/(sales)	38	51
Fair value at December 31	393	315
Pension Benefits - Non-U.S. [Member] \| Private Mortgages [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value at January 1	4	5
Net realized gains/(losses)		(1)
Net unrealized gains/(losses)		1
Net purchases/(sales)		(1)
Fair value at December 31	4	4
Pension Benefits - Non-U.S. [Member] \| Real Estate Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value at January 1	417	413
Net realized gains/(losses)	3
Net unrealized gains/(losses)	6	(4)
Net purchases/(sales)	(29)	8
Fair value at December 31	397	417
Other Postretirement Benefits [Member] \| Private Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value at January 1	5	4
Net unrealized gains/(losses)	2	1
Fair value at December 31	7	5
Other Postretirement Benefits [Member] \| Private Mortgages [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value at January 1	2	3
Net realized gains/(losses)		1
Net purchases/(sales)	(2)	(2)
Fair value at December 31		$ 2

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This element represents purchases, sales, issuances, and settlements (net) which have taken place during the period in relation to assets measured at fair value on a recurring basis using unobservable inputs (Level 3).

+ References

+ Details

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Balance Type:	debit
Period Type:	duration

- Definition

This element represents an asset measured at fair value using significant unobservable inputs (Level 3) which is required for reconciliation purposes of beginning and ending balances.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 157

-Paragraph 32

-Subparagraph c

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6925170&loc=d3e19207-110258

+ Details

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Period Type:	instant

- Definition

Fair Value Measurement With Unobservable Inputs Net Realized Gains Losses

+ References

No definition available.

+ Details

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- Definition

Fair Value Measurement With Unobservable Inputs Net Unrealized Gains Losses

+ References

No definition available.

+ Details

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Namespace Prefix:	xom_
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Balance Type:	debit
Period Type:	duration