Revenues from Contracts with Customers - Disaggregation by Segment (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Revenues from Contracts with Customers - Disaggregation of Revenues
Total fees and other revenues per consolidated statements of operations	$ 1,045.7	$ 1,008.3	$ 3,058.6	$ 3,139.0
Operating Segments
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	725.0	691.7	2,109.1	2,190.1
Operating Segments | Retirement and Income Solutions
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	141.1	133.8	410.9	419.5
Adjustments for fees and other revenues not within the scope of revenue recognition guidance	276.8	273.4	833.2	844.7
Total fees and other revenues per consolidated statements of operations	417.9	407.2	1,244.1	1,264.2
Operating Segments | Principal Asset Management
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	516.2	492.4	1,497.4	1,580.6
Operating Segments | Benefits and Protection
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	23.3	20.7	66.4	59.9
Operating Segments | Corporate
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	44.4	44.8	134.4	130.1
Adjustments for fees and other revenues not within the scope of revenue recognition guidance	(76.9)	(75.2)	(224.2)	(242.8)
Total fees and other revenues per consolidated statements of operations	(32.5)	(30.4)	(89.8)	(112.7)
Operating Segments | Principal Global Investors | Principal Asset Management
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	406.5	395.8	1,168.3	1,277.0
Adjustments for fees and other revenues not within the scope of revenue recognition guidance	9.1	6.4	16.3	20.6
Total fees and other revenues per consolidated statements of operations	415.6	402.2	1,184.6	1,297.6
Operating Segments | Principal International | Principal Asset Management
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	115.1	102.3	345.2	321.9
Adjustments for fees and other revenues not within the scope of revenue recognition guidance	1.4	1.1	4.3	3.4
Total fees and other revenues per consolidated statements of operations	116.5	103.4	349.5	325.3
Operating Segments | Specialty Benefits | Benefits and Protection
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	4.0	3.7	12.0	11.4
Adjustments for fees and other revenues not within the scope of revenue recognition guidance	4.6	4.8	13.7	14.0
Total fees and other revenues per consolidated statements of operations	8.6	8.5	25.7	25.4
Operating Segments | Life Insurance | Benefits and Protection
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	19.4	17.0	54.5	48.6
Adjustments for fees and other revenues not within the scope of revenue recognition guidance	85.7	84.2	246.7	243.3
Total fees and other revenues per consolidated statements of operations	105.1	101.2	301.2	291.9
Operating Segments | Principal Asset Management Eliminations | Principal Asset Management
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	(5.4)	(5.7)	(16.1)	(18.3)
Operating Segments | Benefits And Protection Eliminations | Benefits and Protection
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	(0.1)		(0.1)	(0.1)
Reconciling Items
Revenues from Contracts with Customers - Disaggregation of Revenues
Adjustments for fees and other revenues not within the scope of revenue recognition guidance	300.5	294.5	889.4	882.7
Pre-tax other adjustments	$ 20.2	$ 22.1	$ 60.1	$ 66.2