Debt - Short-Term Debt (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Short-Term Debt
Credit facilities	$ 1,001.4	$ 952.3
Short-term debt	$ 42.9	$ 39.5
Weighted-average interest rates on short-term borrowings (as a percent)	3.90%	4.70%
Credit facility maturing November 2023 \| PFG, PFS, Principal Life as co-borrowers
Short-Term Debt
Credit facilities	$ 600.0
Credit facility maturing November 2023 \| PFG, PFS, Principal Life and Principal Financial Services V (UK) LTD as co-borrowers
Short-Term Debt
Credit facilities	200.0
Credit facility maturing March 2022 \| PFG, PFS, Principal Life as co-borrowers
Short-Term Debt
Credit facilities		$ 600.0
Credit facility maturing March 2022 \| PFG, PFS, Principal Life and Principal Financial Services V (UK) LTD as co-borrowers
Short-Term Debt
Credit facilities		189.0
Credit facility maturing March 2020 \| PFG, PFS, Principal Life and Principal Financial Services V (UK) LTD as co-borrowers
Short-Term Debt
Credit facilities		11.0
Unsecured lines of credit \| Principal International Chile
Short-Term Debt
Credit facilities	141.4	107.3
Short-term debt	42.9	39.5
Unsecured line of credit maturing September 2019 \| Principal Life Insurance Company
Short-Term Debt
Credit facilities	$ 60.0
Unsecured line of credit maturing December 2018 \| Principal Life Insurance Company
Short-Term Debt
Credit facilities		$ 45.0
Commercial paper
Short-Term Debt
Support provided by back-stop facility for commercial paper program (as a percent)	100.00%	100.00%
Back-stop facility outstanding balances	$ 0.0	$ 0.0

Amount of outstanding back-stop facilities as of the balance sheet date.

No definition available.

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- Definition

Percentage of support provided by back-stop facility for commercial paper program.

+ References

No definition available.

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- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

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- Definition

Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(19)(a))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16)(a)(1))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(13))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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- 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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- Definition

Weighted average interest rate of short-term debt outstanding calculated at point in time.

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