XML 105 R90.htm IDEA: XBRL DOCUMENT v3.10.0.1

Pension and Other Postretirement Benefits (Schedule of Net Asset Value Per Share) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Net Asset Value Excluded From Fair Value By Input	$ 767.1	$ 1,032.3
Commingled Funds | Short-Term Money Markets
Defined Benefit Plan Disclosure [Line Items]
Net Asset Value Excluded From Fair Value By Input	$ 23.5	$ 43.5
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	$ 255.6	$ 478.8
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Frequency	Monthly	Monthly
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Notice Period	3 days	3 days
Commingled Funds | International Equities
Defined Benefit Plan Disclosure [Line Items]
Net Asset Value Excluded From Fair Value By Input	$ 122.3	$ 265.1
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Frequency	Monthly	Monthly
Commingled Funds | Fixed Income Funds
Defined Benefit Plan Disclosure [Line Items]
Net Asset Value Excluded From Fair Value By Input	$ 365.7	$ 244.9
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Frequency	Monthly	Monthly
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Notice Period	3 days	3 days
Minimum | Commingled Funds | International Equities
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Notice Period	10 days	14 days
Maximum | Commingled Funds | International Equities
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

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 http://asc.fasb.org/extlink&oid=99377789&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 http://asc.fasb.org/extlink&oid=99377789&loc=SL6742756-110258

+ Details

Name:	us-gaap_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionNoticePeriod1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

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:	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:

X

- Details

Name:	srt_RangeAxis=srt_MinimumMember
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: