XML 75 R59.htm IDEA: XBRL DOCUMENT
v3.22.0.1

Nature of Operations And Summary of Significant Accounting Policies (Narrative) (Details) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2021 USD ($) | Dec. 31, 2020 USD ($) | Dec. 31, 2019 USD ($)
Basis Of Accounting Presentation [Line Items] |  |  |
Number of customers | 3,700,000 |  |
Other than Temporary Impairment Losses, Investments | $ 0.0 | $ 0.0 | $ 0.0
Pre-tax rate for allowance for funds used during construction | 3.30% | 2.60% | 3.00%
Inventory valued using LIFO | $ 44.9 | $ 42.3 |
Excess of replacement over LIFO value | (13.6) | (19.6) |
Inventory valued using the weighted average cost methodology | $ 282.4 | $ 148.8 |

X
- Definition Basis Of Accounting Presentation [Line Items] + References No definition available. + Details
Name: | nix_BasisOfAccountingPresentationLineItems
Namespace Prefix: | nix_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Number of customers + References No definition available. + Details
Name: | nix_NumberOfCustomers
Namespace Prefix: | nix_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Pre tax rate for allowance for funds used during construction + References No definition available. + Details
Name: | nix_PreTaxRateForAllowanceForFundsUsedDuringConstruction
Namespace Prefix: | nix_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition The excess of replacement or current cost over the stated LIFO (last in first out) inventory value when the LIFO inventory method is utilized. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.6(c)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
Name: | us-gaap_ExcessOfReplacementOrCurrentCostsOverStatedLIFOValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The amount by which the fair value of an investment is less than the amortized cost basis or carrying amount of that investment at the balance sheet date and the decline in fair value is deemed to be other than temporary, before considering whether or not such amount is recognized in earnings or other comprehensive income. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 8A -URI http://asc.fasb.org/extlink&oid=124260329&loc=SL6284422-111562 + Details
Name: | us-gaap_ImpairmentOfInvestments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The amount of LIFO (last in first out) inventory present at the reporting date when inventory is also valued using different valuation methods. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6361739&loc=d3e7789-107766 + Details
Name: | us-gaap_LIFOInventoryAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The amount of weighted average cost inventory present at the reporting date when inventory is valued using different valuation methods. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6361739&loc=d3e7789-107766 + Details
Name: | us-gaap_WeightedAverageCostInventoryAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant