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

Amount of revenue resulting from transactions with other operating segments of the same entity.

No definition available.

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

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.

No definition available.

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

Operating revenues is a measure of revenue for the operating segments. It is derived by adjusting total revenues for net realized capital gains and losses (except periodic settlements and accruals on derivatives not designated as hedging instruments), including their impact on recognition of front-end fee revenues, certain market value adjustments to fee revenues and amortization of hedge accounting book value adjustments for certain discontinued hedges, and revenue from the exited group medical insurance business. Operating revenues also includes operating revenues from real estate properties that qualify for discontinued operations.

No definition available.

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

Pre-tax operating earnings is a measure of profit or loss for the operating segments that is used to evaluate performance on a basis comparable to that used by securities analysts. It is derived by adjusting income before income taxes for pre-tax net realized capital gains (losses), as adjusted, pre-tax other adjustments management believes are not indicative of overall operating trends and certain adjustments related to equity method investments.

No definition available.

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

Aggregate earnings recognized during the period for adjustments related to equity method investments and noncontrolling interest.

No definition available.

Name:	pfg_SegmentReportingInformationEarningsAdjustmentsRelatedToEquityMethodInvestmentsAndNoncontrollingInterest
Namespace Prefix:	pfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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

Aggregate revenue recognized during the period for adjustments related to equity method investments.

No definition available.

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

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

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

Name:	us-gaap_StatementBusinessSegmentsAxis=pfg_SegmentRetirementAndIncomeSolutionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_StatementBusinessSegmentsAxis=pfg_SegmentPrincipalGlobalInvestorsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_ConsolidationItemsAxis=us-gaap_OperatingSegmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_SubsegmentsAxis=pfg_SubsegmentRetirementAndIncomeSolutionsFeeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_SubsegmentsAxis=pfg_SubsegmentRetirementAndIncomeSolutionsSpreadMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_StatementBusinessSegmentsAxis=pfg_SegmentPrincipalInternationalMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_StatementBusinessSegmentsAxis=pfg_SegmentUSInsuranceSolutionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_SubsegmentsAxis=pfg_SubsegmentSpecialtyBenefitsInsuranceMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_SubsegmentsAxis=pfg_SubsegmentIndividualLifeInsuranceMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_StatementBusinessSegmentsAxis=pfg_SegmentCorporateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: