XML 161 R144.htm IDEA: XBRL DOCUMENT v2.4.1.9
Postretirement Health Care Plan Estimated Future Benefit Payments (Detail) (Defined Benefit Postretirement Health Coverage, Other Postretirement Plan, USD $)
In Millions, unless otherwise specified
Dec. 31, 2014
Defined Benefit Postretirement Health Coverage | Other Postretirement Plan
 
Schedule of Pension and Other Postretirement Benefits Expected Benefit Payments [Line Items]  
2015 $ 3.0us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
/ ntrs_PostRetirementPlanDisclosuresAxis
= us-gaap_DefinedBenefitPostretirementHealthCoverageMember
2016 3.1us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
/ ntrs_PostRetirementPlanDisclosuresAxis
= us-gaap_DefinedBenefitPostretirementHealthCoverageMember
2017 3.1us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
/ ntrs_PostRetirementPlanDisclosuresAxis
= us-gaap_DefinedBenefitPostretirementHealthCoverageMember
2018 3.1us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
/ ntrs_PostRetirementPlanDisclosuresAxis
= us-gaap_DefinedBenefitPostretirementHealthCoverageMember
2019 3.1us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
/ ntrs_PostRetirementPlanDisclosuresAxis
= us-gaap_DefinedBenefitPostretirementHealthCoverageMember
2020-2024 $ 12.9us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
/ ntrs_PostRetirementPlanDisclosuresAxis
= us-gaap_DefinedBenefitPostretirementHealthCoverageMember