Name:	pfg_ClosedBlockOperationsBenefitClaimsAndSettlementExpenses
Namespace Prefix:	pfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Operating expenses impacting an insurance entity's segregated group of participating or dividend-paying policies and contracts along with the assets allocated to them (known as a closed block).

No definition available.

Name:	pfg_ClosedBlockOperationsOperatingExpenses
Namespace Prefix:	pfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Amounts charged to the closed block during the period necessary to properly fund for certain adjustments, such as face amount and premium increases, due to the adjustable life policies included in the closed block. Also includes other related transfers.

No definition available.

Name:	pfg_FundingAdjustmentsAndOtherTransfers
Namespace Prefix:	pfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Amount of increase (decrease) of closed block liabilities in excess of closed block assets at the date of demutualization.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 805
-Section 50
-Paragraph 3
-Subparagraph (b)(9)
-URI https://asc.fasb.org/extlink&oid=124505872&loc=d3e30806-158569

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 805
-Section 55
-Paragraph 4
-URI https://asc.fasb.org/extlink&oid=124502525&loc=d3e31071-158570

Name:	us-gaap_ClosedBlockAssetsAndLiabilitiesMaximumFutureEarningsToBeRecognizedPeriodIncreaseDecrease
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration

Amount of benefits, claims and expenses that are related to an insurance entity's segregated group of participating or dividend-paying policies and contracts along with the assets allocated to them (known as a closed block). Includes, but is not limited to, death benefits, matured endowments, participating dividends, general expenses and deferred acquisition costs related to the closed block.

Name:	us-gaap_ClosedBlockOperationsBenefitsAndExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- References

No definition available.

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

The amount of income tax expense or benefit allocated to the operations of the closed block for the period.

Name:	us-gaap_ClosedBlockOperationsIncomeTaxes
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Income for the period from the investments allocated to an insurance entity's segregated group of participating or dividend-paying policies and contracts (known as a closed block), net of investment expenses, which are typically reported in a table of closed block operations.

Name:	us-gaap_ClosedBlockOperationsNetInvestmentIncome
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Amount of net income (loss) from operations of the closed block.

Name:	us-gaap_ClosedBlockOperationsNetResults
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

An expense for the period representing distributions paid or accrued for the segregated group of participating or dividend-paying policies and contracts along with the assets allocated to them (known as a closed block), which may be presented in a table of closed block operations as part of summarized financial data.

Name:	us-gaap_ClosedBlockOperationsPolicyholderDividends
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

For the segregated group of participating or dividend-paying policies and contracts along with the assets allocated to them (known as a closed block), revenue for the period from insurance policy premiums; typically included in a table of closed block operations.

Name:	us-gaap_ClosedBlockOperationsPremiums
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Gains and losses realized for the period from the investments allocated to an insurance entity's segregated group of participating or dividend-paying policies and contracts (known as a closed block).

Name:	us-gaap_ClosedBlockOperationsRealizedInvestmentGainsLosses
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

The revenues less expenses from operations of the closed block during the period, before income taxes allocated thereto.

Name:	us-gaap_ClosedBlockOperationsResultsBeforeIncomeTaxes
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Total revenues from an insurance company's segregated group of participating or dividend-paying policies and contracts along with the assets allocated to them (known as a closed block).

Name:	us-gaap_ClosedBlockOperationsRevenue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- References

No definition available.