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

Amount of insurance ceded out of ULSG reserves by affiliated reinsurance subsidiaries in Vermont.

No definition available.

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

Amount of increase (decrease) to the regulatory capital required for the period determined using accounting principles prescribed or permitted by insurance regulators due to use of reporting practice adjustments permitted in reinsurance.

No definition available.

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

Amount of increase (decrease) to the net income for the period determined using accounting principles prescribed or permitted by insurance regulators due to use of reporting practice adjustments permitted in reinsurance.

No definition available.

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

- References

No definition available.

Name:	pfg_StatutoryAccountingPracticesStatutoryNetIncomeAndSurplusAbstract
Namespace Prefix:	pfg_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Amount of statutory reserves assumed by affiliated reinsurance subsidiaries.

No definition available.

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

The amount of statutory capital and surplus (stockholders' equity) as of the balance sheet date using prescribed or permitted statutory accounting practices (rather than GAAP, if different) of the state or country.

Reference 1: 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)(23)(c))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478777/944-210-S99-1

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 944
-SubTopic 505
-Section 50
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477908/944-505-50-1

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

Amount of net income for the period determined using accounting principles prescribed or permitted by insurance regulators.