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

The amount of adjustment to net realized capital losses related to certain variable annuity fees.

No definition available.

Name:	pfg_CertainVariableAnnuityFees
Namespace Prefix:	pfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Adjustment to move amounts reported in operating expenses and benefits, claims and settlement expenses to net realized capital gains (losses) for segment profit (loss) reporting related to the portion of amortization expense from deferred acquisition costs and other actuarial balances, respectively, attributable to the portion of estimated gross profits related to net realized capital gains (losses).

No definition available.

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

Net impact to revenue of (1) adjustment for periodic settlements and accruals on derivatives not designated as hedging instruments to move that amount from net realized capital gains (losses) to net investment income for segment profit (loss) reporting, (2) adjustment for mark-to-market adjustments on derivatives and hedged items to move that amount from net investment income to net realized capital gains (losses) for segment profit (loss) reporting and (3) amortization of the cumulative fair value adjustment for assets that have had fair value hedge accounting terminated to move that amount from net investment income to net realized capital gains (losses) for segment profit (loss) reporting.

No definition available.

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

Adjustment to move amounts reported in net investment income to net realized capital gains (losses) for segment profit (loss) reporting related to equity method investments.

No definition available.

Name:	pfg_EquityMethodInvestmentsRelatedAdjustments
Namespace Prefix:	pfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Adjustment to net realized capital gains (losses) related to market value adjustments of market risk benefits.

No definition available.

Name:	pfg_MarketValueAdjustmentOfMarketRiskBenefits
Namespace Prefix:	pfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Adjustment for the portion of the change in fair value of embedded derivatives related to customer behavior-related impacts, which is a risk we assume, to move that amount to benefits, claims and settlement expenses for segment profit (loss) reporting.

No definition available.

Name:	pfg_MarketValueAdjustmentsEmbeddedDerivatives
Namespace Prefix:	pfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- References

No definition available.

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

Net realized capital gains (losses) net of recognition of deferred front-end fee revenues for sales charges on retirement products and services and certain market value adjustments to fee revenues. It excludes periodic settlements and accruals on derivatives not designated as hedging instruments.

No definition available.

Name:	pfg_SegmentReportingInformationNetRealizedCapitalGainsLosses
Namespace Prefix:	pfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Pre-tax net realized capital gains (losses) are net of related changes in the amortization pattern of deferred acquisition costs and related actuarial balances, recognition of deferred front-end fee revenues for sales charges on retirement and life insurance products and services, amortization of hedge accounting book value adjustments for certain discontinued hedges, net realized capital gains and losses distributed, noncontrolling interest capital gains and losses, certain adjustments related to seed money and certain market value adjustments to fee revenues. Pre-tax net realized capital gains (losses), as adjusted, exclude periodic settlements and accruals on derivative instruments not designated as hedging instruments and exclude certain market value adjustments of embedded derivatives and realized capital gains (losses) associated with our exited group medical insurance business.

No definition available.

Name:	pfg_SegmentReportingInformationPretaxNetRealizedCapitalGainsLossesNetOfAdjustments
Namespace Prefix:	pfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Adjustment to move amounts reported in net investment income to net realized capital gains (losses) for segment profit (loss) reporting related to sponsored investment funds.

No definition available.

Name:	pfg_SponsoredInvestmentFundsRelatedAdjustments
Namespace Prefix:	pfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Amount of realized and unrealized gain (loss) on investment.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (c)
-URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27405-111563

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.7(c),9(a))
-URI https://asc.fasb.org/extlink&oid=126953954&loc=SL114868664-224227

Reference 3: http://www.xbrl.org/2003/role/recommendedDisclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=126954810&loc=d3e3602-108585