2.2.0.7 false Other Assets (Details) (USD $) 0606 - Disclosure - Other Assets (Details) true false In Millions false false 1 USD false false Pure Standard http://www.xbrl.org/2003/instance pure xbrli 0 USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 Shares Standard http://www.xbrl.org/2003/instance shares xbrli 0 $ 3 Summary of Company's unamortized investment balance, remaining commitments and maximum exposure to loss related to low-income housing partnership 1 bni_SummaryOfCompanysUnamortizedInvestmentBalanceRemainingCommitmentsAndMaximumExposureToLossRelatedToLowIncomeHousingPartnershipAbstract bni false na duration Summary Of Companys Unamortized Investment Balance Remaining Commitments And Maximum Exposure To Loss Related To Low Income... false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false xbrli:stringItemType string Summary Of Companys Unamortized Investment Balance Remaining Commitments And Maximum Exposure To Loss Related To Low Income Housing Partnership Abstract. false 4 Unamortized investment balance classified as Other Assets 2 us-gaap_VariableInterestEntityCarryingAmountOfCollateralizedAssetsUnconsolidatedVIE us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 true true false false 577000000 577 false false false xbrli:monetaryItemType monetary The carrying amount of the assets in the enterprise's statement of financial position that relate to the enterprise's variable interest in the unconsolidated variable interest entity. In general, a VIE is a corporation, partnership, trust, or any other legal structure used for business purposes that either (a) does not have equity investors with voting rights or (b) has equity investors that do not provide sufficient financial resources for the entity to support its activities. A VIE often holds financial assets, including loans or receivables, real estate or other property. A VIE may be essentially passive or it may engage in research and development or other activities on behalf of another company. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name FASB Interpretation (FIN) -Number 46R -Paragraph 23 -Subparagraph b Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name FASB Staff Position (FSP) -Number FAS140-4 and FIN46(R)-8 -Paragraph C6 -Subparagraph a false 5 Remaining commitments classified as Other Liabilities 2 us-gaap_VariableInterestEntityCarryingAmountOfCollateralizedLiabilitiesUnconsolidatedVIE us-gaap true credit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 148000000 148 false false false xbrli:monetaryItemType monetary The carrying amount of the liabilities in the enterprise's statement of financial position that relate to the enterprise's variable interest in the unconsolidated variable interest entity. In general, a VIE is a corporation, partnership, trust, or any other legal structure used for business purposes that either (a) does not have equity investors with voting rights or (b) has equity investors that do not provide sufficient financial resources for the entity to support its activities. A VIE often holds financial assets, including loans or receivables, real estate or other property. A VIE may be essentially passive or it may engage in research and development or other activities on behalf of another company. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name FASB Interpretation (FIN) -Number 46R -Paragraph 23 -Subparagraph b Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name FASB Staff Position (FSP) -Number FAS140-4 and FIN46(R)-8 -Paragraph C6 -Subparagraph a false 6 Maximum exposure to loss 2 us-gaap_VariableInterestMaximumExposureToLoss us-gaap true credit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 577000000 577 false false false xbrli:monetaryItemType monetary Quantifies the entity's maximum exposure to loss. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name FASB Staff Position (FSP) -Number FAS140-4 and FIN46(R)-8 -Paragraph C6 -Subparagraph c false 7 Other Assets (Textuals) [Abstract] 1 bni_OtherAssetsTextualsAbstract bni false na duration Other Assets Textuals Abstract. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false xbrli:stringItemType string Other Assets Textuals Abstract. false 8 The Company's ownership percentage of investment in low-income housing partnership 2 bni_CompanysOwnershipPercentageOfInvestmentInLowIncomeHousingPartnership bni false na duration The Company's ownership percentage of investment in low-income housing partnership. false false false false false false false false false false false verboselabel false 1 false true false false 0.999 0.999 false false false us-types:percentItemType pure The Company's ownership percentage of investment in low-income housing partnership. No authoritative reference available. false 9 The unrelated General Partner's ownership percentage of investment in low income housing partnership 2 bni_UnrelatedGeneralPartnersOwnershipPercentageOfInvestmentInLowIncomeHousingPartnership bni false na duration The unrelated General Partner's ownership percentage of investment in low-income housing partnership. false false false false false false false false false false false verboselabel false 1 false true false false 0.001 0.001 false false false us-types:percentItemType pure The unrelated General Partner's ownership percentage of investment in low-income housing partnership. No authoritative reference available. false 10 Total assets of low-income housing partnership 2 bni_TotalAssetsOfLowIncomeHousingPartnership bni false debit instant Total assets of low-income housing partnership, which represents the size of the VIE. false false false false false false false false false false false verboselabel false 1 false true false false 740000000 740 false false false xbrli:monetaryItemType monetary Total assets of low-income housing partnership, which represents the size of the VIE. No authoritative reference available. false 11 Investment commitments to be paid in 2012 2 bni_InvestmentCommitmentsToBePaidInYearTwoThousandTwelve bni false credit duration Investment commitments to be paid in 2012. false false false false false false false false false false false verboselabel false 1 false true false false 130000000 130 false false false xbrli:monetaryItemType monetary Investment commitments to be paid in 2012. No authoritative reference available. false 12 Investment commitments to be paid in 2013 2 bni_InvestmentCommitmentsToBePaidInYearTwoThousandThirteen bni false credit duration Investment commitments to be paid in 2013. false false false false false false false false false false false verboselabel false 1 true true false false 18000000 18 false false false xbrli:monetaryItemType monetary Investment commitments to be paid in 2013. No authoritative reference available. false 1 10 false Millions UnKnown UnKnown false true