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Incentive Distributions Specified Target Levels (Detail) (USD $)
 12 Months Ended
Dec. 31, 2014
Incentive Distribution Made To Managing Member Or General Partner [Line Items]  
General partner 2.00%wpz_GeneralPartnerMarginalInterestInDistributions
Maximum  
Incentive Distribution Made To Managing Member Or General Partner [Line Items]  
General partner 50.00%wpz_GeneralPartnerMarginalInterestInDistributions
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
Minimum Quarterly Distribution  
Incentive Distribution Made To Managing Member Or General Partner [Line Items]  
Total quarterly distribution per unit 0.3375wpz_CommonUnitDistributionsPerUnitPaid
/ us-gaap_DistributionsMadeToMemberOrLimitedPartnerByDistributionTypeAxis
= wpz_MinimumQuarterlyDistributionMember
Unitholders 98.00%wpz_LimitedPartnerMarginalInterestInDistributions
/ us-gaap_DistributionsMadeToMemberOrLimitedPartnerByDistributionTypeAxis
= wpz_MinimumQuarterlyDistributionMember
General partner 2.00%wpz_GeneralPartnerMarginalInterestInDistributions
/ us-gaap_DistributionsMadeToMemberOrLimitedPartnerByDistributionTypeAxis
= wpz_MinimumQuarterlyDistributionMember
First Target Distribution | Maximum  
Incentive Distribution Made To Managing Member Or General Partner [Line Items]  
Total quarterly distribution per unit 0.388125wpz_CommonUnitDistributionsPerUnitPaid
/ us-gaap_DistributionsMadeToMemberOrLimitedPartnerByDistributionTypeAxis
= wpz_FirstTargetDistributionMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
Unitholders 98.00%wpz_LimitedPartnerMarginalInterestInDistributions
/ us-gaap_DistributionsMadeToMemberOrLimitedPartnerByDistributionTypeAxis
= wpz_FirstTargetDistributionMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
General partner 2.00%wpz_GeneralPartnerMarginalInterestInDistributions
/ us-gaap_DistributionsMadeToMemberOrLimitedPartnerByDistributionTypeAxis
= wpz_FirstTargetDistributionMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
Second Target Distribution | Minimum  
Incentive Distribution Made To Managing Member Or General Partner [Line Items]  
Total quarterly distribution per unit 0.388125wpz_CommonUnitDistributionsPerUnitPaid
/ us-gaap_DistributionsMadeToMemberOrLimitedPartnerByDistributionTypeAxis
= wpz_SecondTargetDistributionMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
Unitholders 85.00%wpz_LimitedPartnerMarginalInterestInDistributions
/ us-gaap_DistributionsMadeToMemberOrLimitedPartnerByDistributionTypeAxis
= wpz_SecondTargetDistributionMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
General partner 15.00%wpz_GeneralPartnerMarginalInterestInDistributions
/ us-gaap_DistributionsMadeToMemberOrLimitedPartnerByDistributionTypeAxis
= wpz_SecondTargetDistributionMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
Second Target Distribution | Maximum  
Incentive Distribution Made To Managing Member Or General Partner [Line Items]  
Total quarterly distribution per unit 0.421875wpz_CommonUnitDistributionsPerUnitPaid
/ us-gaap_DistributionsMadeToMemberOrLimitedPartnerByDistributionTypeAxis
= wpz_SecondTargetDistributionMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
Third Target Distribution | Minimum  
Incentive Distribution Made To Managing Member Or General Partner [Line Items]  
Total quarterly distribution per unit 0.421875wpz_CommonUnitDistributionsPerUnitPaid
/ us-gaap_DistributionsMadeToMemberOrLimitedPartnerByDistributionTypeAxis
= wpz_ThirdTargetDistributionMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
Unitholders 75.00%wpz_LimitedPartnerMarginalInterestInDistributions
/ us-gaap_DistributionsMadeToMemberOrLimitedPartnerByDistributionTypeAxis
= wpz_ThirdTargetDistributionMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
General partner 25.00%wpz_GeneralPartnerMarginalInterestInDistributions
/ us-gaap_DistributionsMadeToMemberOrLimitedPartnerByDistributionTypeAxis
= wpz_ThirdTargetDistributionMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
Third Target Distribution | Maximum  
Incentive Distribution Made To Managing Member Or General Partner [Line Items]  
Total quarterly distribution per unit 0.50625wpz_CommonUnitDistributionsPerUnitPaid
/ us-gaap_DistributionsMadeToMemberOrLimitedPartnerByDistributionTypeAxis
= wpz_ThirdTargetDistributionMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
Thereafter | Minimum  
Incentive Distribution Made To Managing Member Or General Partner [Line Items]  
Total quarterly distribution per unit 0.50625wpz_CommonUnitDistributionsPerUnitPaid
/ us-gaap_DistributionsMadeToMemberOrLimitedPartnerByDistributionTypeAxis
= wpz_TargetDistributionThereafterMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
Unitholders 50.00%wpz_LimitedPartnerMarginalInterestInDistributions
/ us-gaap_DistributionsMadeToMemberOrLimitedPartnerByDistributionTypeAxis
= wpz_TargetDistributionThereafterMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
General partner 50.00%wpz_GeneralPartnerMarginalInterestInDistributions
/ us-gaap_DistributionsMadeToMemberOrLimitedPartnerByDistributionTypeAxis
= wpz_TargetDistributionThereafterMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember