Revenues from Contracts with Customers - Disaggregation by Segment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Revenues from Contracts with Customers - Disaggregation of Revenues
Total fees and other revenues per consolidated statements of operations	$ 4,095.9	$ 4,137.8	$ 5,041.3
Operating Segments
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	2,814.9	2,875.8	3,150.1
Operating Segments | Retirement and Income Solutions
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	556.3	551.4	590.1
Adjustments for fees and other revenues not within the scope of revenue recognition guidance	1,118.7	1,114.0	1,226.9
Total fees and other revenues per consolidated statements of operations	1,675.0	1,665.4	1,817.0
Operating Segments | Principal Asset Management
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	1,989.6	2,077.6	2,254.6
Operating Segments | Benefits and Protection
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	89.8	80.1	75.3
Operating Segments | Corporate
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	179.2	166.7	230.1
Adjustments for fees and other revenues not within the scope of revenue recognition guidance	(299.0)	(312.6)	(359.3)
Total fees and other revenues per consolidated statements of operations	(119.8)	(145.9)	(129.2)
Operating Segments | Principal Global Investors | Principal Asset Management
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	1,554.1	1,675.0	1,787.9
Adjustments for fees and other revenues not within the scope of revenue recognition guidance	24.9	27.4	36.2
Total fees and other revenues per consolidated statements of operations	1,579.0	1,702.4	1,824.1
Operating Segments | Principal International | Principal Asset Management
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	456.5	426.3	492.7
Adjustments for fees and other revenues not within the scope of revenue recognition guidance	5.8	4.5	4.2
Total fees and other revenues per consolidated statements of operations	462.3	430.8	496.9
Operating Segments | Specialty Benefits | Benefits and Protection
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	15.9	15.1	14.9
Adjustments for fees and other revenues not within the scope of revenue recognition guidance	18.2	18.6	19.0
Total fees and other revenues per consolidated statements of operations	34.1	33.7	33.9
Operating Segments | Life Insurance | Benefits and Protection
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	74.0	65.1	60.6
Adjustments for fees and other revenues not within the scope of revenue recognition guidance	333.3	321.5	885.0
Total fees and other revenues per consolidated statements of operations	407.3	386.6	945.6
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)	(0.2)
Operating Segments | Principal Asset Management Eliminations | Principal Asset Management
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	(21.0)	(23.7)	(26.0)
Reconciling Items
Revenues from Contracts with Customers - Disaggregation of Revenues
Adjustments for fees and other revenues not within the scope of revenue recognition guidance	1,200.5	1,172.8	1,811.3
Pre-tax other adjustments	$ 80.5	$ 89.2	$ 79.9