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Segment Information - Depreciation and Amortization Expense by Segment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Segment Information: Depreciation and amortization expense
Depreciation and amortization expense	$ 208.0	$ 186.6	$ 166.8
Retirement and Income Solutions
Segment Information: Depreciation and amortization expense
Depreciation and amortization expense	81.7	69.1	48.2
Principal Global Investors
Segment Information: Depreciation and amortization expense
Depreciation and amortization expense	21.1	21.6	18.9
Principal International
Segment Information: Depreciation and amortization expense
Depreciation and amortization expense	57.3	56.0	58.6
U.S. Insurance Solutions
Segment Information: Depreciation and amortization expense
Depreciation and amortization expense	24.2	25.1	25.0
Corporate
Segment Information: Depreciation and amortization expense
Depreciation and amortization expense	$ 23.7	$ 14.8	$ 16.1

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- Definition

The current period expense charged against earnings on long-lived, physical assets not used in production, and which are not intended for resale, to allocate or recognize the cost of such assets over their useful lives; or to record the reduction in book value of an intangible asset over the benefit period of such asset; or to reflect consumption during the period of an asset that is not used in production.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3602-108585

+ Details

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X

- Definition

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.

+ References

No definition available.

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