Revenues from Contracts with Customers - Disaggregation within Segments (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Revenues from Contracts with Customers - Disaggregation of Revenues
Total fees and other revenues	$ 1,052.9	$ 995.3
Premiums and other considerations	1,684.6	1,448.6
Net investment income (loss)	1,072.2	986.7
Operating Segments
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	738.5	685.1
Total operating revenues	3,804.7	3,439.6
Operating Segments | Benefits and Protection
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	24.7	20.6
Total operating revenues	1,185.9	1,103.4
Operating Segments | Benefits and Protection | Specialty Benefits
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	3.8	3.9
Fees and other revenues not within the scope of revenue recognition guidance	4.6	4.6
Total fees and other revenues	8.4	8.5
Premiums and other considerations	792.9	733.6
Net investment income (loss)	47.0	40.1
Total operating revenues	848.3	782.2
Operating Segments | Benefits and Protection | Specialty Benefits | Administrative service fee revenue
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	3.8	3.9
Operating Segments | Benefits and Protection | Life Insurance
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	20.9	16.7
Fees and other revenues not within the scope of revenue recognition guidance	84.2	77.3
Total fees and other revenues	105.1	94.0
Premiums and other considerations	128.9	130.8
Net investment income (loss)	103.8	96.6
Total operating revenues	337.8	321.4
Operating Segments | Benefits and Protection | Life Insurance | Administrative service fee revenue
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	7.9	7.2
Operating Segments | Benefits and Protection | Life Insurance | Commission income
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	13.0	9.5
Operating Segments | Principal Asset Management
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	496.6	489.2
Total operating revenues	655.3	692.5
Operating Segments | Principal Asset Management | Principal Global Investors
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	389.0	381.3
Fees and other revenues not within the scope of revenue recognition guidance	5.4	4.6
Total fees and other revenues	394.4	385.9
Net investment income (loss)	10.4	6.8
Total operating revenues	404.8	392.7
Operating Segments | Principal Asset Management | Principal Global Investors | Management fee revenue
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	352.3	339.7
Operating Segments | Principal Asset Management | Principal Global Investors | Other fee revenue
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	36.7	41.6
Operating Segments | Principal Asset Management | Principal International
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	113.5	113.2
Fees and other revenues not within the scope of revenue recognition guidance	1.3	1.4
Total fees and other revenues	114.8	114.6
Premiums and other considerations	2.0	6.4
Net investment income (loss)	139.9	184.1
Total operating revenues	256.7	305.1
Operating Segments | Principal Asset Management | Principal International | Latin America
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	86.7	85.9
Operating Segments | Principal Asset Management | Principal International | Asia
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	27.0	27.5
Operating Segments | Principal Asset Management | Principal International | Geographical Eliminations
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	(0.2)	(0.2)
Operating Segments | Principal Asset Management | Principal International | Management fee revenue
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	111.0	110.9
Operating Segments | Principal Asset Management | Principal International | Other fee revenue
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	2.5	2.3
Operating Segments | Retirement and Income Solutions
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	159.3	130.2
Fees and other revenues not within the scope of revenue recognition guidance	279.3	278.3
Total fees and other revenues	438.6	408.5
Premiums and other considerations	765.6	582.7
Net investment income (loss)	728.2	624.9
Total operating revenues	1,932.4	1,616.1
Operating Segments | Retirement and Income Solutions | Administrative service fee revenue
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	155.5	126.5
Operating Segments | Retirement and Income Solutions | Deposit account fee revenue
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	3.1	2.9
Operating Segments | Retirement and Income Solutions | Other fee revenue
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers		0.4
Operating Segments | Retirement and Income Solutions | Commission income
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	0.7	0.4
Operating Segments | Corporate
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	57.9	45.1
Fees and other revenues not within the scope of revenue recognition guidance	(79.3)	(75.6)
Total fees and other revenues	(21.4)	(30.5)
Premiums and other considerations	(1.3)	(1.3)
Net investment income (loss)	53.8	59.4
Total operating revenues	31.1	27.6
Operating Segments | Corporate | Other fee revenue
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	21.7	20.5
Operating Segments | Corporate | Commission income
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	105.5	87.9
Operating Segments | Corporate | Revenue by type - Eliminations
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	$ (69.3)	$ (63.3)