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Investments - Real Estate (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Real estate
Depreciation expense on invested real estate	$ 67.4	$ 65.3	$ 60.0
Accumulated depreciation on invested real estate	$ 652.0	$ 591.2

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- Definition

Amount of depreciation expense on real estate for the period.

+ References

No definition available.

+ Details

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

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- Definition

The amount as of the balance sheet date of accumulated depreciation pertaining to invested real estate.

+ References

No definition available.

+ Details

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

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- References

No definition available.

+ Details

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