Revenues from Contracts with Customers - Disaggregation by Segment (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Revenues from Contracts with Customers - Disaggregation of Revenues
Total fees and other revenues per consolidated statements of operations	$ 1,082.6	$ 1,061.4	$ 2,160.3	$ 2,114.3
Operating Segments
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	750.0	750.6	1,495.8	1,489.1
Operating Segments \| Retirement and Income Solutions
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	148.2	164.7	293.9	324.0
Adjustments for fees and other revenues not within the scope of revenue recognition guidance	286.0	275.5	581.5	554.8
Total fees and other revenues per consolidated statements of operations	434.2	440.2	875.4	878.8
Operating Segments \| Principal Asset Management
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	519.6	502.0	1,034.3	998.6
Operating Segments \| Benefits and Protection
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	26.7	28.1	51.5	52.8
Operating Segments \| Corporate
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	55.5	55.8	116.1	113.7
Adjustments for fees and other revenues not within the scope of revenue recognition guidance	(78.1)	(77.8)	(157.0)	(157.1)
Total fees and other revenues per consolidated statements of operations	(22.6)	(22.0)	(40.9)	(43.4)
Operating Segments \| Investment Management \| Principal Asset Management
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	433.1	412.9	859.8	820.0
Adjustments for fees and other revenues not within the scope of revenue recognition guidance	9.8	5.6	12.6	10.8
Total fees and other revenues per consolidated statements of operations	442.9	418.5	872.4	830.8
Operating Segments \| International Pension \| Principal Asset Management
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	91.4	93.6	183.8	186.9
Adjustments for fees and other revenues not within the scope of revenue recognition guidance	1.5	1.5	2.7	2.8
Total fees and other revenues per consolidated statements of operations	92.9	95.1	186.5	189.7
Operating Segments \| Specialty Benefits \| Benefits and Protection
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	4.0	4.0	7.7	7.8
Adjustments for fees and other revenues not within the scope of revenue recognition guidance	4.1	4.4	8.7	9.0
Total fees and other revenues per consolidated statements of operations	8.1	8.4	16.4	16.8
Operating Segments \| Life Insurance \| Benefits and Protection
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	22.7	24.2	43.8	45.1
Adjustments for fees and other revenues not within the scope of revenue recognition guidance	91.8	82.5	181.4	166.7
Total fees and other revenues per consolidated statements of operations	114.5	106.7	225.2	211.8
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)
Operating Segments \| Principal Asset Management Eliminations \| Principal Asset Management
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	(4.9)	(4.5)	(9.3)	(8.3)
Reconciling items
Revenues from Contracts with Customers - Disaggregation of Revenues
Adjustments for fees and other revenues not within the scope of revenue recognition guidance	315.4	291.7	629.9	586.8
Pre-tax other adjustments	$ 17.2	$ 19.1	$ 34.6	$ 38.4