Revenues from Contracts with Customers - Disaggregation by Segment (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Revenues from Contracts with Customers - Disaggregation of Revenues
Total fees and other revenues per consolidated statements of operations	$ 1,015.7	$ 1,251.8	$ 3,178.3	$ 3,711.0
Operating Segments
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	692.9	796.5	2,194.2	2,329.8
Operating Segments | Retirement and Income Solutions
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	133.8	146.6	419.5	441.0
Operating Segments | Principal Global Investors
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	395.8	453.5	1,277.0	1,303.6
Adjustments for fees and other revenues not within the scope of revenue recognition guidance	6.4	11.0	20.6	27.1
Total fees and other revenues per consolidated statements of operations	402.2	464.5	1,297.6	1,330.7
Operating Segments | Principal International
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	102.3	125.1	321.9	373.5
Adjustments for fees and other revenues not within the scope of revenue recognition guidance	1.1	1.0	3.4	3.1
Total fees and other revenues per consolidated statements of operations	103.4	126.1	325.3	376.6
Operating Segments | U.S. Insurance Solutions
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	20.7	19.7	59.9	55.8
Operating Segments | Corporate
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	40.3	51.6	115.9	155.9
Adjustments for fees and other revenues not within the scope of revenue recognition guidance	(76.6)	(91.8)	(247.4)	(266.3)
Total fees and other revenues per consolidated statements of operations	(36.3)	(40.2)	(131.5)	(110.4)
Operating Segments | Retirement and Income Solutions - Fee | Retirement and Income Solutions
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	130.8	144.2	411.0	433.8
Adjustments for fees and other revenues not within the scope of revenue recognition guidance	291.3	324.1	900.5	964.3
Total fees and other revenues per consolidated statements of operations	422.1	468.3	1,311.5	1,398.1
Operating Segments | Retirement and Income Solutions - Spread | Retirement and Income Solutions
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	3.0	2.4	8.5	7.2
Adjustments for fees and other revenues not within the scope of revenue recognition guidance	0.9	2.1	2.1	6.8
Total fees and other revenues per consolidated statements of operations	3.9	4.5	10.6	14.0
Operating Segments | Specialty Benefits insurance | U.S. Insurance Solutions
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	3.7	3.9	11.4	11.4
Adjustments for fees and other revenues not within the scope of revenue recognition guidance	4.8	5.4	14.0	14.9
Total fees and other revenues per consolidated statements of operations	8.5	9.3	25.4	26.3
Operating Segments | Individual Life insurance | U.S. Insurance Solutions
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	17.0	15.8	48.6	44.5
Adjustments for fees and other revenues not within the scope of revenue recognition guidance	91.3	204.1	253.3	635.8
Total fees and other revenues per consolidated statements of operations	108.3	219.9	301.9	680.3
Operating Segments | U.S. Insurance Solutions Eliminations | U.S. Insurance Solutions
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	319.2	455.9	946.5	1,385.7
Pre-tax other adjustments	$ 3.6	$ (0.6)	$ 37.6	$ (4.5)