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

Amount of transfer to (from) liability for separate account (to) from general account.

No definition available.

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

Amount of separate account liability payable to policyholder upon surrender of contract before maturity.

Name:	us-gaap_SeparateAccountLiabilityCashSurrenderValueAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of increase (decrease) in separate account liability from performance of investment.

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

Amount increase (decrease) in separate account liability from change, classified as other.

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

Amount of decrease in separate account liability from policy charge.

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

Amount of cash inflow to separate account liability from premium and deposit from cash received.

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

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

No definition available.

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

Amount of liability for variable contract in which all or portion of contract holder's funds is allocated to specific separate account and supported by assets held in separate account.

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 944
-SubTopic 80
-Name Accounting Standards Codification
-Section 55
-Paragraph 18
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480078/944-80-55-18

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 80
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480109/944-80-50-2

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 80
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480141/944-80-45-2

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(18))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479440/944-210-S99-1

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 80
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480109/944-80-50-2