Name:	pfg_FairValueOptionAggregateUnpaidPrincipalAmountsOfObligationsForWhichFairValueOptionWasElected
Namespace Prefix:	pfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

The contractual principal amounts of commercial mortgage loans of consolidated variable interest entities for which the fair value option was elected.

No definition available.

Name:	pfg_FairValueOptionContractualPrincipalAmountsOfAssetsForWhichFairValueOptionWasElected
Namespace Prefix:	pfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

The fair value of commercial mortgage loans of consolidated variable interest entities and equity method investments for which the fair value option was elected.

No definition available.

Name:	pfg_FairValueOptionFairValueOfAssetsForWhichFairValueOptionWasElected
Namespace Prefix:	pfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

The fair value of liabilities of consolidated variable interest entities for which the fair value option was elected.

No definition available.

Name:	pfg_FairValueOptionFairValueOfLiabilitiesForWhichFairValueOptionWasElected
Namespace Prefix:	pfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Represents the number of loans, which are more than 90 days past due or in nonaccrual status.

No definition available.

Name:	pfg_NumberOfLoansMoreThan90DaysPastDue
Namespace Prefix:	pfg_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

For each line item in the statement of financial position, the amounts of gains and losses from fair value changes included in earnings.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 30

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6957238&loc=d3e14172-108612

Name:	us-gaap_FairValueOptionChangesInFairValueGainLoss1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

This item represents the estimated amount of gains or losses included in earnings during the period attributable to changes in instrument-specific credit risk arising from loans and other receivables held as assets.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 30

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=6957238&loc=d3e14172-108612

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

This item represents the estimated amount of gains and losses from fair value changes included in earnings that are attributable to changes in the instrument-specific credit risk of liabilities with fair values that have been significantly affected during the reporting period by changes in the instrument-specific credit risk.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 30

-Subparagraph (d)(1)

-URI http://asc.fasb.org/extlink&oid=6957238&loc=d3e14172-108612

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

Name:	us-gaap_FairValueOptionQuantitativeDisclosuresLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Represents the total of interest and dividend income, including any amortization and accretion (as applicable) of discounts and premiums, earned from (1) loans and leases whether held-for-sale or held-in-portfolio; (2) investment securities; (3) federal funds sold; (4) securities purchased under agreements to resell; (5) investments in banker's acceptances, commercial paper, or certificates of deposit; (6) dividend income; or (7) other investments not otherwise specified herein.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-04.1-5)

-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph 1, 2 , 3, 4, 5

-Article 9

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

Amount of the cost of borrowed funds accounted for as interest expense.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 20

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6450988&loc=d3e26243-108391

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-04.9)

-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph 9

-Article 9

Name:	us-gaap_InterestExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Name:	us-gaap_EligibleItemOrGroupForFairValueOptionAxis=pfg_CommercialMortgageLoansOfConsolidatedVariableInterestEntitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_EligibleItemOrGroupForFairValueOptionAxis=pfg_ObligationsOfConsolidatedVariableInterestEntitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: