Investments - Gross Unrealized Losses for Fixed Maturities (Details) $ in Millions	Sep. 30, 2026 USD ($) item	Dec. 31, 2025 USD ($) item
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	$ 27,331.1	$ 6,056.3
Fixed maturities, Less than twelve months, Gross unrealized losses	999.7	125.7
Fixed maturities, Greater than or equal to twelve months, Fair value	28,016.0	33,571.0
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	6,870.2	5,096.3
Fixed maturities, Total, Fair value	55,347.1	39,627.3
Fixed maturities, Total, Gross unrealized losses	7,869.9	5,222.0
U.S. government and agencies
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	1,380.0	484.1
Fixed maturities, Less than twelve months, Gross unrealized losses	77.3	11.0
Fixed maturities, Greater than or equal to twelve months, Fair value	752.2	734.1
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	341.6	257.1
Fixed maturities, Total, Fair value	2,132.2	1,218.2
Fixed maturities, Total, Gross unrealized losses	418.9	268.1
Non-U.S. governments
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	57.3	12.8
Fixed maturities, Less than twelve months, Gross unrealized losses	2.8	0.3
Fixed maturities, Greater than or equal to twelve months, Fair value	180.0	310.9
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	55.7	54.3
Fixed maturities, Total, Fair value	237.3	323.7
Fixed maturities, Total, Gross unrealized losses	58.5	54.6
States and political subdivisions
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	2,237.9	639.4
Fixed maturities, Less than twelve months, Gross unrealized losses	147.6	8.9
Fixed maturities, Greater than or equal to twelve months, Fair value	4,322.0	4,903.5
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	1,357.8	1,003.0
Fixed maturities, Total, Fair value	6,559.9	5,542.9
Fixed maturities, Total, Gross unrealized losses	1,505.4	1,011.9
Corporate debt securities
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	10,723.9	1,889.9
Fixed maturities, Less than twelve months, Gross unrealized losses	459.1	95.7
Fixed maturities, Greater than or equal to twelve months, Fair value	16,048.5	19,474.6
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	4,109.4	2,970.8
Fixed maturities, Total, Fair value	26,772.4	21,364.5
Fixed maturities, Total, Gross unrealized losses	4,568.5	3,066.5
Residential mortgage-backed pass-through securities
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	2,426.1	201.2
Fixed maturities, Less than twelve months, Gross unrealized losses	107.4	0.7
Fixed maturities, Greater than or equal to twelve months, Fair value	892.1	1,147.6
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	158.2	117.3
Fixed maturities, Total, Fair value	3,318.2	1,348.8
Fixed maturities, Total, Gross unrealized losses	265.6	118.0
Commercial mortgage-backed securities
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	2,081.6	342.0
Fixed maturities, Less than twelve months, Gross unrealized losses	62.2	2.5
Fixed maturities, Greater than or equal to twelve months, Fair value	2,971.0	3,465.9
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	340.2	301.6
Fixed maturities, Total, Fair value	5,052.6	3,807.9
Fixed maturities, Total, Gross unrealized losses	402.4	304.1
Collateralized debt obligations
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	2,196.6	1,919.9
Fixed maturities, Less than twelve months, Gross unrealized losses	5.2	4.7
Fixed maturities, Greater than or equal to twelve months, Fair value	46.3	20.2
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	4.9	5.0
Fixed maturities, Total, Fair value	2,242.9	1,940.1
Fixed maturities, Total, Gross unrealized losses	10.1	9.7
Other debt obligations
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	6,227.7	567.0
Fixed maturities, Less than twelve months, Gross unrealized losses	138.1	1.9
Fixed maturities, Greater than or equal to twelve months, Fair value	2,803.9	3,514.2
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	502.4	387.2
Fixed maturities, Total, Fair value	9,031.6	4,081.2
Fixed maturities, Total, Gross unrealized losses	640.5	389.1
Principal Life Insurance Company
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	26,978.0	5,888.1
Fixed maturities, Less than twelve months, Gross unrealized losses	981.6	117.8
Fixed maturities, Greater than or equal to twelve months, Fair value	27,884.4	32,859.9
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	6,828.0	5,032.1
Fixed maturities, Total, Fair value	54,862.4	38,748.0
Fixed maturities, Total, Gross unrealized losses	$ 7,809.6	$ 5,149.9
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure
Available-for-sale Securities in Unrealized Loss Positions, Qualitative Disclosure, Percent Investment Grade (as a percent)	97.00%	97.00%
Available-for-sale Securities in Unrealized Loss Positions, Qualitative Disclosure, Average Price (percent of carrying value to amortized cost)	88.00%	88.00%
Available-for-sale Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less Than Twelve Months \| item	3,132	870
Available-for-sale Securities in Unrealized Loss Positions, Average Price, Less Than Twelve Months (percent of carrying value to amortized cost)	96.00%	98.00%
Available-for-sale Securities in Unrealized Loss Positions, Percent Investment Grade, Less Than Twelve Months (as a percent)	96.00%	93.00%
Available-for-sale Securities in Unrealized Loss Position, Aggregate Losses On Investment Grade Investments, Less Than Twelve Months	$ 941.4	$ 96.7
Available-for-sale Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Twelve Months or Longer \| item	5,345	5,758
Available-for-sale Securities in Unrealized Loss Positions, Average Price, Twelve Months or Longer (percent of carrying value to amortized cost)	80.00%	87.00%
Principal Life Insurance Company \| States and political subdivisions
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	$ 1,345.0	$ 996.0
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure
Available-for-sale Securities in Unrealized Loss Positions, Average Price, Twelve Months or Longer (percent of carrying value to amortized cost)	76.00%	83.00%
Principal Life Insurance Company \| Corporate debt securities
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	$ 4,085.6	$ 2,919.0
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure
Available-for-sale Securities in Unrealized Loss Positions, Average Price, Twelve Months or Longer (percent of carrying value to amortized cost)	80.00%	87.00%
Principal Life Insurance Company \| Commercial mortgage-backed securities
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	$ 339.4	$ 301.0
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure
Available-for-sale Securities in Unrealized Loss Positions, Average Price, Twelve Months or Longer (percent of carrying value to amortized cost)	90.00%	92.00%
Principal Life Insurance Company \| Collateralized mortgage obligation security
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	$ 471.2	$ 356.7
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure
Available-for-sale Securities in Unrealized Loss Positions, Average Price, Twelve Months or Longer (percent of carrying value to amortized cost)	81.00%	87.00%

No definition available.

Name:	pfg_AvailableForSaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureAbstract
Namespace Prefix:	pfg_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

This item contains disclosure of the unrealized losses on investments in available-for-sale debt securities (without an allowance for credit loss) that have been in an unrealized loss position less than twelve months and deemed to be investment grade.

+ References

No definition available.

+ Details

Name:	pfg_DebtSecuritiesAvailableForSaleSecuritiesWithoutAllowanceForCreditLossContinuousUnrealizedLossPositionAggregateLossesOnInvestmentGradeInvestmentsLessThanTwelveMonths
Namespace Prefix:	pfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

This item contains disclosure of the average price of investments in available-for-sale debt securities that are in an unrealized loss position without an allowance for credit loss. It is the calculated result of dividing the carrying value by amortized cost.

+ References

No definition available.

+ Details

Name:	pfg_DebtSecuritiesAvailableForSaleSecuritiesWithoutAllowanceForCreditLossUnrealizedLossPositionsAveragePrice
Namespace Prefix:	pfg_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

This item contains disclosure of the average price of investments in available-for-sale debt securities without an allowance for credit loss that have been in a loss position for less than twelve months. It is the calculated result of dividing the carrying value by amortized cost.

+ References

No definition available.

+ Details

Name:	pfg_DebtSecuritiesAvailableForSaleSecuritiesWithoutAllowanceForCreditLossUnrealizedLossPositionsAveragePriceLessThanTwelveMonths
Namespace Prefix:	pfg_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

This item contains disclosure of the average price of investments in available-for-sale debt securities without an allowance for credit loss that have been in an unrealized loss position for greater than or equal to twelve months. It is the calculated result of dividing the carrying value by amortized cost.

+ References

No definition available.

+ Details

Name:	pfg_DebtSecuritiesAvailableForSaleSecuritiesWithoutAllowanceForCreditLossUnrealizedLossPositionsAveragePriceTwelveMonthsOrLonger
Namespace Prefix:	pfg_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

This item contains disclosure of the percent of investments in available-for-sale debt securities that are investment grade and in an unrealized loss position without an allowance for credit loss.

+ References

No definition available.

+ Details

Name:	pfg_DebtSecuritiesAvailableForSaleSecuritiesWithoutAllowanceForCreditLossUnrealizedLossPositionsPercentInvestmentGrade
Namespace Prefix:	pfg_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

This item contains disclosure of the percent of investments in available-for-sale debt securities that are investment grade without an allowance for credit loss and have been in an unrealized loss position for less than twelve months.

+ References

No definition available.

+ Details

Name:	pfg_DebtSecuritiesAvailableForSaleSecuritiesWithoutAllowanceForCreditLossUnrealizedLossPositionsPercentInvestmentGradeLessThanTwelveMonths
Namespace Prefix:	pfg_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- 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

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValueAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 326
-SubTopic 30
-Name Accounting Standards Codification
-Section 55
-Paragraph 8
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479081/326-30-55-8

Reference 2: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 7
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-7

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479106/326-30-50-5

+ Details

Name:	us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 7
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-7

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479106/326-30-50-5

+ Details

Name:	us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Number of investments in debt securities measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer, without an allowance for credit loss. Includes beneficial interest in securitized financial asset.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 326
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (b)(3)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479106/326-30-50-4

+ Details

Name:	us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerNumberOfPositions
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

+ References

+ Details

Name:	us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

+ References

+ Details

Name:	us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Number of investments in debt securities measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without an allowance for credit loss. Includes beneficial interest in securitized financial asset.

+ References

+ Details

Name:	us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsNumberOfPositions
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position without allowance for credit loss.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 326
-SubTopic 30
-Name Accounting Standards Codification
-Section 55
-Paragraph 8
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479081/326-30-55-8

Reference 2: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-6

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479106/326-30-50-4

+ Details

Name:	us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Subparagraph (a)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-6

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (a)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479106/326-30-50-4

+ Details

Name:	us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_USTreasuryAndGovernmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_ForeignGovernmentDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_USStatesAndPoliticalSubdivisionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CorporateDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_ResidentialMortgageBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CommercialMortgageBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CollateralizedDebtObligationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_OtherDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=pfg_PrincipalLifeInsuranceCompanyConsolidatedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_MortgageBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: