Employee Benefits - Weighted-average assumptions used to determine future benefit obligations (Details)
|
Dec. 31, 2014
|
Dec. 31, 2013
|
U.K. [Member] |
|
|
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |
|
|
Discount rate |
3.70%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_ForeignPensionPlansDefinedBenefitMember |
4.55%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_ForeignPensionPlansDefinedBenefitMember |
Underlying price inflation |
1.95%aon_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationUnderlyingPriceInflation / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_ForeignPensionPlansDefinedBenefitMember |
2.40%aon_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationUnderlyingPriceInflation / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_ForeignPensionPlansDefinedBenefitMember |
U.K. [Member] | Minimum [Member] |
|
|
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |
|
|
Discount rate |
3.35%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_ForeignPensionPlansDefinedBenefitMember / us-gaap_RangeAxis = us-gaap_MinimumMember |
3.70%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_ForeignPensionPlansDefinedBenefitMember / us-gaap_RangeAxis = us-gaap_MinimumMember |
U.K. [Member] | Maximum [Member] |
|
|
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |
|
|
Discount rate |
4.05%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_ForeignPensionPlansDefinedBenefitMember / us-gaap_RangeAxis = us-gaap_MaximumMember |
4.40%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_ForeignPensionPlansDefinedBenefitMember / us-gaap_RangeAxis = us-gaap_MaximumMember |
U.S. [Member] | Minimum [Member] |
|
|
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |
|
|
Discount rate |
3.37%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_UnitedStatesPensionPlansOfUSEntityDefinedBenefitMember / us-gaap_RangeAxis = us-gaap_MinimumMember |
3.97%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_UnitedStatesPensionPlansOfUSEntityDefinedBenefitMember / us-gaap_RangeAxis = us-gaap_MinimumMember |
U.S. [Member] | Maximum [Member] |
|
|
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |
|
|
Discount rate |
4.08%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_UnitedStatesPensionPlansOfUSEntityDefinedBenefitMember / us-gaap_RangeAxis = us-gaap_MaximumMember |
4.87%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_UnitedStatesPensionPlansOfUSEntityDefinedBenefitMember / us-gaap_RangeAxis = us-gaap_MaximumMember |
Other [Member] | Minimum [Member] |
|
|
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |
|
|
Discount rate |
2.03%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPensionPlansDefinedBenefitMember / us-gaap_RangeAxis = us-gaap_MinimumMember |
3.60%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPensionPlansDefinedBenefitMember / us-gaap_RangeAxis = us-gaap_MinimumMember |
Rate of compensation increase |
2.25%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationRateOfCompensationIncrease / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPensionPlansDefinedBenefitMember / us-gaap_RangeAxis = us-gaap_MinimumMember |
2.25%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationRateOfCompensationIncrease / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPensionPlansDefinedBenefitMember / us-gaap_RangeAxis = us-gaap_MinimumMember |
Underlying price inflation |
2.00%aon_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationUnderlyingPriceInflation / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPensionPlansDefinedBenefitMember / us-gaap_RangeAxis = us-gaap_MinimumMember |
1.50%aon_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationUnderlyingPriceInflation / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPensionPlansDefinedBenefitMember / us-gaap_RangeAxis = us-gaap_MinimumMember |
Other [Member] | Maximum [Member] |
|
|
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |
|
|
Discount rate |
3.91%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPensionPlansDefinedBenefitMember / us-gaap_RangeAxis = us-gaap_MaximumMember |
4.71%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPensionPlansDefinedBenefitMember / us-gaap_RangeAxis = us-gaap_MaximumMember |
Rate of compensation increase |
3.50%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationRateOfCompensationIncrease / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPensionPlansDefinedBenefitMember / us-gaap_RangeAxis = us-gaap_MaximumMember |
3.50%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationRateOfCompensationIncrease / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPensionPlansDefinedBenefitMember / us-gaap_RangeAxis = us-gaap_MaximumMember |
Underlying price inflation |
2.50%aon_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationUnderlyingPriceInflation / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPensionPlansDefinedBenefitMember / us-gaap_RangeAxis = us-gaap_MaximumMember |
2.50%aon_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationUnderlyingPriceInflation / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPensionPlansDefinedBenefitMember / us-gaap_RangeAxis = us-gaap_MaximumMember |