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

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:	instant

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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 30
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=75031198&loc=d3e14172-108612

Name:	us-gaap_FairValueOptionChangesInFairValueGainLoss1
Namespace Prefix:	us-gaap_
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:	us-gaap_FairValueOptionQuantitativeDisclosuresLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Amount of operating interest income, including, but not limited to, amortization and accretion of premiums and discounts on securities.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1(e))
-URI http://asc.fasb.org/extlink&oid=116634182&loc=SL114868664-224227