Amount of depreciation expense on real estate for the period.

No definition available.

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- 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

- Definition

The net realized gains or losses on investments during the period, net of tax, not including gains or losses on securities separately or otherwise categorized as trading, available-for-sale, or held-to-maturity.

+ References

No definition available.

+ Details

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

- References

No definition available.

+ Details

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

- Definition

The net realized gains or losses on investments during the period, not including gains or losses on securities separately or otherwise categorized as trading, available-for-sale, or held-to-maturity.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04.3(a))
-URI http://asc.fasb.org/extlink&oid=116637232&loc=SL114874131-224263

+ Details

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Balance Type:	credit
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- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Investments - Real Estate (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
Investments - Real Estate (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Real estate
Depreciation expense on invested real estate		$ 60.0	$ 54.1	$ 55.9
Accumulated depreciation on invested real estate		$ 526.0	$ 487.2
Certain real estate joint ventures
Real estate
Net pre-tax realized capital gain	$ 690.9
Net after-tax realized capital gain	$ 410.8