Name:	pfg_AvailableForSaleDebtSecuritiesGrossRealizedGain
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Period Type:	duration

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_
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Balance Type:	credit
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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Period Type:	duration

This item represents the gross realized losses realized on the sale of equity 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 equity securities.

No definition available.

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Name:	pfg_AvailableForSaleSecuritiesGrossRealizedGainsLossesSaleProceedsAbstract
Namespace Prefix:	pfg_
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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
Balance Type:	credit
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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Balance Type:	credit
Period Type:	duration

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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Balance Type:	credit
Period Type:	duration

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
Balance Type:	credit
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

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-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.

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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

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-Section 50

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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

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

-Publisher SEC

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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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-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.

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Before tax amount of other than temporary impairment (OTTI) on a debt security, categorized as available-for-sale, recognized in other comprehensive income (loss).

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

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

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

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 130

-Paragraph 17

-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.