Name:	pfg_CapitalGainsLossesDistributed
Namespace Prefix:	pfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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 deferred policy acquisition cost amortization and sales inducement amortization, respectively, attributable to the portion of estimated gross profits related to net realized capital gains (losses).

No definition available.

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

Net impact 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 and (2) 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 fees and other revenues to net realized capital gains (losses) for segment profit (loss) reporting related to amortization of unearned revenue reserves attributable to the portion of estimated gross profits related to net realized capital gains (losses).

No definition available.

Name:	pfg_FrontEndFeeRevenuesRecognition
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

Adjustment to move amounts reported in fees and other revenues to net realized capital gains (losses) for segment profit (loss) reporting related to participating contract cashout gains/losses related to net realized capital losses/gains on the sale of invested assets used to fund the cashout of the contract at market value.

No definition available.

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

Adjustment for net realized capital gains and losses associated with an exited group medical insurance business to move that amount to other after-tax adjustments for segment profit (loss) reporting.

No definition available.

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

Adjustment for the income tax effect of the pre-tax net realized capital gains (losses), as adjusted.

No definition available.

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

Adjustment for the portion of net income attributable to noncontrolling interest related to net realized capital gains (losses).

No definition available.

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

- Details

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

Net realized capital gains (losses) net of income taxes, related changes in the amortization pattern of deferred policy acquisition costs and sales inducements, recognition of deferred front-end fee revenues for sales charges on retirement products and services, net realized capital gains and losses distributed, noncontrolling interest capital gains and losses and certain market value adjustments to fee revenues. 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.

No definition available.

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

This item represents the net total realized and unrealized gain (loss) included in earnings for the period as a result of selling or holding marketable securities categorized as trading, available-for-sale, or held-to-maturity, including the unrealized holding gain (loss) of held-to-maturity securities transferred to the trading security category and the cumulative unrealized gain (loss) which was included in other comprehensive income (a separate component of shareholders' equity) for available-for-sale securities transferred to trading securities during the period. Additionally, this item would include any gains (losses) realized during the period from the sale of investments accounted for under the cost method of accounting and losses recognized for other than temporary impairments (OTTI) of the subject investments.

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 210.5-03.7(c),9(a))

-URI http://asc.fasb.org/extlink&oid=6880815&loc=d3e20235-122688

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 9

-Subparagraph (c)-(e)

-URI http://asc.fasb.org/extlink&oid=6872113&loc=d3e27357-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3602-108585

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 10

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6872113&loc=d3e27405-111563

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 28

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 7

-Article 5

Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 13, 22

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.