Revenues from Contracts with Customers - Disaggregation by Segment (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Revenues from Contracts with Customers - Disaggregation of Revenues
Total fees and other revenues per consolidated statements of operations	$ 947.6	$ 1,265.3	$ 2,162.6	$ 2,459.2
Operating Segments
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	749.6	795.2	1,501.3	1,533.3
Operating Segments | Retirement and Income Solutions
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	141.3	150.1	285.7	294.4
Operating Segments | Principal Global Investors
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	451.6	444.0	881.2	850.1
Adjustments for fees and other revenues not within the scope of revenue recognition guidance	8.9	8.1	14.2	16.1
Total fees and other revenues per consolidated statements of operations	460.5	452.1	895.4	866.2
Operating Segments | Principal International
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	109.2	126.5	219.6	248.4
Adjustments for fees and other revenues not within the scope of revenue recognition guidance	1.1	1.1	2.3	2.1
Total fees and other revenues per consolidated statements of operations	110.3	127.6	221.9	250.5
Operating Segments | U.S. Insurance Solutions
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	19.8	18.7	39.2	36.1
Operating Segments | Corporate
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	27.7	55.9	75.6	104.3
Adjustments for fees and other revenues not within the scope of revenue recognition guidance	(79.4)	(88.5)	(170.8)	(174.5)
Total fees and other revenues per consolidated statements of operations	(51.7)	(32.6)	(95.2)	(70.2)
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	138.5	147.7	280.2	289.6
Adjustments for fees and other revenues not within the scope of revenue recognition guidance	290.9	326.5	609.2	640.2
Total fees and other revenues per consolidated statements of operations	429.4	474.2	889.4	929.8
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	2.8	2.4	5.5	4.8
Adjustments for fees and other revenues not within the scope of revenue recognition guidance	0.1	2.7	1.2	4.7
Total fees and other revenues per consolidated statements of operations	2.9	5.1	6.7	9.5
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	3.8	7.7	7.5
Adjustments for fees and other revenues not within the scope of revenue recognition guidance	4.5	4.7	9.2	9.5
Total fees and other revenues per consolidated statements of operations	8.2	8.5	16.9	17.0
Operating Segments | Individual Life insurance | U.S. Insurance Solutions
Revenues from Contracts with Customers - Disaggregation of Revenues
Total segment revenue from contracts with customers	16.2	15.0	31.6	28.7
Adjustments for fees and other revenues not within the scope of revenue recognition guidance	(64.0)	211.5	162.0	431.7
Total fees and other revenues per consolidated statements of operations	(47.8)	226.5	193.6	460.4
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)	(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	162.1	466.1	627.3	929.8
Pre-tax other adjustments	$ 35.9	$ 4.0	$ 34.0	$ (3.9)