Revenues from Contracts with Customers - Disaggregation by Segment (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Revenues from Contracts with Customers - Disaggregation of Revenues
Total fees and other revenues per consolidated statements of operations	$ 1,017.6	$ 911.5	$ 2,012.9	$ 2,130.7
Operating Segments
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	699.0	748.2	1,384.1	1,498.4
Operating Segments \| Retirement and Income Solutions
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	139.6	141.3	269.8	285.7
Adjustments for fees and other revenues not within the scope of revenue recognition guidance	278.1	271.9	556.4	571.3
Total fees and other revenues per consolidated statements of operations	417.7	413.2	826.2	857.0
Operating Segments \| Principal Asset Management
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	492.0	554.8	981.2	1,088.2
Operating Segments \| Benefits and Protection
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	22.5	19.8	43.1	39.2
Operating Segments \| Corporate
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	44.9	32.3	90.0	85.3
Adjustments for fees and other revenues not within the scope of revenue recognition guidance	(71.7)	(77.9)	(147.3)	(167.6)
Total fees and other revenues per consolidated statements of operations	(26.8)	(45.6)	(57.3)	(82.3)
Operating Segments \| Principal Global Investors \| Principal Asset Management
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	380.5	451.6	761.8	881.2
Adjustments for fees and other revenues not within the scope of revenue recognition guidance	2.6	8.9	7.2	14.2
Total fees and other revenues per consolidated statements of operations	383.1	460.5	769.0	895.4
Operating Segments \| Principal International \| Principal Asset Management
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	116.9	109.2	230.1	219.6
Adjustments for fees and other revenues not within the scope of revenue recognition guidance	1.5	1.1	2.9	2.3
Total fees and other revenues per consolidated statements of operations	118.4	110.3	233.0	221.9
Operating Segments \| Specialty Benefits \| Benefits and Protection
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	4.1	3.7	8.0	7.7
Adjustments for fees and other revenues not within the scope of revenue recognition guidance	4.5	4.5	9.1	9.2
Total fees and other revenues per consolidated statements of operations	8.6	8.2	17.1	16.9
Operating Segments \| Life Insurance \| Benefits and Protection
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	18.4	16.2	35.1	31.6
Adjustments for fees and other revenues not within the scope of revenue recognition guidance	83.7	(69.2)	161.0	159.1
Total fees and other revenues per consolidated statements of operations	102.1	(53.0)	196.1	190.7
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)	(6.0)	(10.7)	(12.6)
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)
Reconciling Items
Revenues from Contracts with Customers - Disaggregation of Revenues
Adjustments for fees and other revenues not within the scope of revenue recognition guidance	298.5	139.2	588.9	588.2
Pre-tax other adjustments	$ 20.1	$ 24.1	$ 39.9	$ 44.1