v2.4.0.6

Employee Benefit Plans - Pension and Postretirement Plans (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified | Dec. 31, 2011 | Dec. 31, 2010
--- | --- | ---
U.S. (Pension Benefits) [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Accumulated benefit obligation | $ 5,363 | $ 4,905
Int'l (Pension Benefits) [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Accumulated benefit obligation | $ 2,939 | $ 2,711

X
- Definition Accumulated Benefit Obligation + References No definition available. + Details
Name: | cop_AccumulatedBenefitObligation
Namespace Prefix: | cop_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Details
Name: | us-gaap_DefinedBenefitPlanDisclosureLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration