Revenues from Contracts with Customers - Disaggregation by Segment (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Revenues from Contracts with Customers - Disaggregation of Revenues
Total fees and other revenues per consolidated statements of operations	$ 1,215.0	$ 1,193.9
Operating Segments
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	751.7	738.1
Operating Segments | Retirement and Income Solutions
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	144.4	144.3
Operating Segments | Principal Global Investors
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	429.6	406.1
Fees and other revenues not within the scope of revenue recognition guidance	5.3	8.0
Total fees and other revenues per consolidated statements of operations	434.9	414.1
Operating Segments | Principal International
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	110.4	121.9
Fees and other revenues not within the scope of revenue recognition guidance	1.2	1.0
Total fees and other revenues per consolidated statements of operations	111.6	122.9
Operating Segments | U.S. Insurance Solutions
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	19.4	17.4
Operating Segments | Corporate
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	47.9	48.4
Fees and other revenues not within the scope of revenue recognition guidance	(91.4)	(86.0)
Total fees and other revenues per consolidated statements of operations	(43.5)	(37.6)
Operating Segments | Retirement and Income Solutions - Fee | Retirement and Income Solutions
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	141.7	141.9
Fees and other revenues not within the scope of revenue recognition guidance	318.3	313.7
Total fees and other revenues per consolidated statements of operations	460.0	455.6
Operating Segments | Retirement and Income Solutions - Spread | Retirement and Income Solutions
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	2.7	2.4
Fees and other revenues not within the scope of revenue recognition guidance	1.1	2.0
Total fees and other revenues per consolidated statements of operations	3.8	4.4
Operating Segments | Specialty Benefits insurance | U.S. Insurance Solutions
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	4.0	3.7
Fees and other revenues not within the scope of revenue recognition guidance	4.7	4.8
Total fees and other revenues per consolidated statements of operations	8.7	8.5
Operating Segments | Individual Life insurance | U.S. Insurance Solutions
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	15.4	13.7
Fees and other revenues not within the scope of revenue recognition guidance	226.0	220.2
Total fees and other revenues per consolidated statements of operations	241.4	233.9
Reconciling Items
Revenues from Contracts with Customers - Disaggregation of Revenues
Fees and other revenues not within the scope of revenue recognition guidance	465.2	463.7
Pre-tax other adjustments	$ (1.9)	$ (7.9)