Name:	pfg_AvailableForSaleDebtSecuritiesGrossRealizedGain
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Data Type:	xbrli:monetaryItemType
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This item represents the gross realized losses realized on the sale of debt securities categorized neither as held-to-maturity nor trading securities. Additionally, this item would include any losses recognized for other than temporary impairments of the subject investments in debt securities.

No definition available.

Name:	pfg_AvailableForSaleDebtSecuritiesGrossRealizedLoss
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

This item represents the net gains/losses on available-for-sale debt securities that are the hedged item in a designated fair value hedge.

No definition available.

Name:	pfg_AvailableForSaleDebtSecuritiesHedgingNet
Namespace Prefix:	pfg_
Data Type:	xbrli:monetaryItemType
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Period Type:	duration

- Details

Name:	pfg_AvailableForSaleDebtSecuritiesNetRealizedCapitalGainsAbstract
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This item represents the gross realized gains realized on the sale of equity securities categorized neither as held-to-maturity nor trading securities.

No definition available.

Name:	pfg_AvailableForSaleEquitySecuritiesGrossRealizedGain
Namespace Prefix:	pfg_
Data Type:	xbrli:monetaryItemType
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Name:	pfg_AvailableForSaleSecuritiesGrossRealizedGainsLossesSaleProceedsAbstract
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This item represents the net realized gains/losses on the sale of mortgage loans. Additionally, this item includes gains/losses related to changes in the mortgage loan reserve/valuation allowance to cover probable credit losses on the loan portfolio.

No definition available.

Name:	pfg_MortgageLoanRealizedGainLoss
Namespace Prefix:	pfg_
Data Type:	xbrli:monetaryItemType
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Period Type:	duration

This item represents the net gains/losses realized from the sale and unrealized holding gains/losses for invested assets (e.g., real estate, seed money) not classified as fixed maturities, equity securities, mortgage loans or derivatives. Additionally, this item includes foreign currency exchange gains/losses.

No definition available.

Name:	pfg_OtherRealizedGainLoss
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Trading securities represent securities that are bought and held principally for the purpose of selling them in the near term (thus held for only a short period of time). This item represents the net gains/losses realized from the sale, exchange, redemption or retirement of debt securities held as trading and the unrealized holding gains/losses for these securities.

No definition available.

Name:	pfg_TradingDebtSecuritiesRealizedGainLoss
Namespace Prefix:	pfg_
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Trading securities represent securities that are bought and held principally for the purpose of selling them in the near term (thus held for only a short period of time). This item represents the net gains/losses realized from the sale, exchange, redemption or retirement of equity securities held as trading and the unrealized holding gains/losses for these securities.

No definition available.

Name:	pfg_TradingEquitySecuritiesRealizedGainLoss
Namespace Prefix:	pfg_
Data Type:	xbrli:monetaryItemType
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Period Type:	duration

The total amount of proceeds received for the sale of securities, categorized neither as held-to-maturity nor trading securities, during the reporting period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 9

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27357-111563

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Data Type:	xbrli:monetaryItemType
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Aggregate net gain (loss) on all derivative instruments recognized in earnings during the period, before tax effects.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4A

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5618551-113959

Name:	us-gaap_GainLossOnDerivativeInstrumentsNetPretax
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Data Type:	xbrli:monetaryItemType
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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 230

-SubTopic 10

-Section 45

-Paragraph 28

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

Reference 2: 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=26872669&loc=d3e20235-122688

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

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-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27405-111563

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 7

-Article 5

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

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-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27357-111563

Name:	us-gaap_GainLossOnInvestments
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Data Type:	xbrli:monetaryItemType
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Amount before tax of other than temporary impairment (OTTI) on investment in available-for-sale debt security, recognized in other comprehensive loss.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 35

-Paragraph 35

-URI http://asc.fasb.org/extlink&oid=27723805&loc=d3e25362-111560

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 220

-SubTopic 10

-Section 45

-Paragraph 10A

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-URI http://asc.fasb.org/extlink&oid=28358780&loc=SL7669646-108580