Revenues from Contracts with Customers - Disaggregation by Segment (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Revenues from Contracts with Customers - Disaggregation of Revenues
Total fees and other revenues per consolidated statements of operations	$ 1,061.4	$ 1,017.6	$ 2,114.3	$ 2,012.9
Operating Segments
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	750.6	699.0	1,489.1	1,384.1
Operating Segments \| Retirement and Income Solutions
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	164.7	139.6	324.0	269.8
Adjustments for fees and other revenues not within the scope of revenue recognition guidance	275.5	278.1	554.8	556.4
Total fees and other revenues per consolidated statements of operations	440.2	417.7	878.8	826.2
Operating Segments \| Principal Asset Management
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	502.0	492.0	998.6	981.2
Operating Segments \| Benefits and Protection
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	28.1	22.5	52.8	43.1
Operating Segments \| Corporate
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	55.8	44.9	113.7	90.0
Adjustments for fees and other revenues not within the scope of revenue recognition guidance	(77.8)	(71.7)	(157.1)	(147.3)
Total fees and other revenues per consolidated statements of operations	(22.0)	(26.8)	(43.4)	(57.3)
Operating Segments \| Principal Global Investors \| Principal Asset Management
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	392.5	380.5	781.5	761.8
Adjustments for fees and other revenues not within the scope of revenue recognition guidance	5.9	2.6	11.3	7.2
Total fees and other revenues per consolidated statements of operations	398.4	383.1	792.8	769.0
Operating Segments \| Principal International \| Principal Asset Management
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	113.9	116.9	227.4	230.1
Adjustments for fees and other revenues not within the scope of revenue recognition guidance	1.5	1.5	2.8	2.9
Total fees and other revenues per consolidated statements of operations	115.4	118.4	230.2	233.0
Operating Segments \| Specialty Benefits \| Benefits and Protection
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	4.0	4.1	7.8	8.0
Adjustments for fees and other revenues not within the scope of revenue recognition guidance	4.4	4.5	9.0	9.1
Total fees and other revenues per consolidated statements of operations	8.4	8.6	16.8	17.1
Operating Segments \| Life Insurance \| Benefits and Protection
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	24.2	18.4	45.1	35.1
Adjustments for fees and other revenues not within the scope of revenue recognition guidance	82.5	83.7	166.7	161.0
Total fees and other revenues per consolidated statements of operations	106.7	102.1	211.8	196.1
Operating Segments \| Eliminations \| Benefits and Protection
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	(0.1)		(0.1)
Operating Segments \| Principal Asset Management Eliminations \| Principal Asset Management
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	(4.4)	(5.4)	(10.3)	(10.7)
Reconciling items
Revenues from Contracts with Customers - Disaggregation of Revenues
Adjustments for fees and other revenues not within the scope of revenue recognition guidance	291.7	298.5	586.8	588.9
Pre-tax other adjustments	$ 19.1	$ 20.1	$ 38.4	$ 39.9