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Other Commitments And Contingencies Other Commitments and Contingencies (Insurance Recoveries and Cash Collected (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended | 16 Months Ended | 25 Months Ended
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Sep. 30, 2020 | Sep. 30, 2020 | Dec. 31, 2019 | Sep. 30, 2020
Commitments and Contingencies Disclosure [Abstract] |  |  |  |
Insurance recoveries recorded | $ 0 | $ 0 | $ 800 | $ 800
Cash collected from insurance recoveries |  |  |  | $ (800)

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- Definition Proceeds From Insurance Settlement + References No definition available. + Details
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Namespace Prefix: | nix_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- References No definition available. + Details
Name: | us-gaap_CommitmentsAndContingenciesDisclosureAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition The amount recovered from insurance. These recoveries reduce costs and losses that are reported as a separate line item under operating expenses. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.3) -URI http://asc.fasb.org/extlink&oid=120395209&loc=SL114868664-224227 + Details
Name: | us-gaap_InsuranceRecoveries
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration