XML 116 R93.htm IDEA: XBRL DOCUMENT
v3.22.4

Pension and Other Postretirement Benefits (Schedule of Net Asset Value Per Share) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2022 | Dec. 31, 2021
Defined Benefit Plan Disclosure [Line Items] |  |
Net Asset Value Excluded From Fair Value By Input | $ 607.5 | $ 778.8
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments | 11.6 | 12.1
Private Equity and Real Estate Limited Partnerships |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Net Asset Value Excluded From Fair Value By Input | 13.7 | 20.4
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments | 11.6 | 12.1
Commingled Funds | Short-Term Money Markets |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Net Asset Value Excluded From Fair Value By Input | 63.6 | 60.8
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments | $ 0.0 | $ 0.0
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Frequency | Daily | Daily
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Notice Period | 1 day | 1 day
Commingled Funds | United States Equities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Net Asset Value Excluded From Fair Value By Input | $ 144.4 | $ 210.7
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments | $ 0.0 | $ 0.0
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Frequency | Daily | Daily
Commingled Funds | United States Equities | Maximum |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Notice Period | 5 days | 5 days
Commingled Funds | United States Equities | Minimum |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Notice Period | 1 day | 1 day
Commingled Funds | International Equities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Net Asset Value Excluded From Fair Value By Input | $ 109.9 | $ 137.8
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments | $ 0.0 | $ 0.0
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Frequency | Monthly | Monthly
Commingled Funds | International Equities | Maximum |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Notice Period | 30 days | 30 days
Commingled Funds | International Equities | Minimum |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Notice Period | 10 days | 10 days
Commingled Funds | Fixed Income Funds |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Net Asset Value Excluded From Fair Value By Input | $ 275.9 | $ 349.1
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments | $ 0.0 | $ 0.0
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Frequency | Daily | Daily
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Notice Period | 3 days | 3 days

X
- Definition Net Asset Value Excluded From Fair Value By Input + References No definition available. + Details
Name: | nix_NetAssetValueExcludedFromFairValueByInput
Namespace Prefix: | nix_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_DefinedBenefitPlanDisclosureLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition States the frequency (for example, annually, semi-annually, quarterly) with which the entity can redeem its investment, or portion thereof, for each of those certain investments for which net asset value per share is calculated (including by unit, membership interest, or other equity (ownership interest) unit measure) (alternative investments), by major category. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 6A -Subparagraph (d) -URI https://asc.fasb.org/extlink&oid=126976982&loc=SL6742756-110258 + Details
Name: | us-gaap_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequency
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Notice period the entity is required to deliver before it can redeem an investment calculated using net asset value per share, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Includes, but is not limited to, investments calculated by per unit, per membership interest, other equity or ownership interest and alternative investments. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 6A -Subparagraph (d) -URI https://asc.fasb.org/extlink&oid=126976982&loc=SL6742756-110258 + Details
Name: | us-gaap_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionNoticePeriod1
Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition The amount of unfunded commitments for which the entity is obligated, to those certain investments for which net asset value per share is calculated (including by unit, membership interest, or other equity (ownership interest) unit measure) (alternative investments). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 6A -Subparagraph (c) -URI https://asc.fasb.org/extlink&oid=126976982&loc=SL6742756-110258 + Details
Name: | us-gaap_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareUnfundedCommittments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=nix_PrivateEquityAndRealEstateLimitedPartnershipsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=nix_CommingledFundsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=nix_ShortTermMoneyMarketsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=nix_UnitedStatesEquitiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=nix_InternationalEquitiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_FixedIncomeFundsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |