Revenues from Contracts with Customers - Disaggregation within Segments (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Revenues from Contracts with Customers - Disaggregation of Revenues
Total fees and other revenues	$ 1,045.7	$ 1,008.3	$ 3,058.6	$ 3,139.0
Premiums and other considerations	1,457.9	1,486.5	4,399.2	3,740.1
Net investment income (loss)	989.2	911.7	2,964.0	2,857.1
Operating Segments
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	725.0	691.7	2,109.1	2,190.1
Total operating revenues	3,478.0	3,422.4	10,418.1	9,813.5
Operating Segments | Benefits and Protection
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	23.3	20.7	66.4	59.9
Total operating revenues	1,151.4	1,085.8	3,380.1	3,232.5
Operating Segments | Benefits and Protection | Specialty Benefits
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	4.0	3.7	12.0	11.4
Fees and other revenues not within the scope of revenue recognition guidance	4.6	4.8	13.7	14.0
Total fees and other revenues	8.6	8.5	25.7	25.4
Premiums and other considerations	762.7	704.0	2,237.9	2,056.4
Net investment income (loss)	45.3	36.5	127.4	136.5
Total operating revenues	816.6	749.0	2,391.0	2,218.3
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	4.0	3.7	12.0	11.4
Operating Segments | Benefits and Protection | Life Insurance
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	19.4	17.0	54.5	48.6
Fees and other revenues not within the scope of revenue recognition guidance	85.7	84.2	246.7	243.3
Total fees and other revenues	105.1	101.2	301.2	291.9
Premiums and other considerations	136.7	142.7	394.4	415.1
Net investment income (loss)	93.2	93.0	294.0	307.6
Total operating revenues	335.0	336.9	989.6	1,014.6
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	8.9	7.0	23.6	20.9
Operating Segments | Benefits and Protection | Life Insurance | Commission income
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	10.5	10.0	30.9	27.7
Operating Segments | Principal Asset Management
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	516.2	492.4	1,497.4	1,580.6
Total operating revenues	668.8	783.0	2,048.2	2,441.3
Operating Segments | Principal Asset Management | Principal Global Investors
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	406.5	395.8	1,168.3	1,277.0
Fees and other revenues not within the scope of revenue recognition guidance	9.1	6.4	16.3	20.6
Total fees and other revenues	415.6	402.2	1,184.6	1,297.6
Net investment income (loss)	9.0	3.8	22.8	7.3
Total operating revenues	424.6	406.0	1,207.4	1,304.9
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	348.2	351.7	1,028.8	1,095.2
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	58.3	44.1	139.5	181.8
Operating Segments | Principal Asset Management | Principal International
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	115.1	102.3	345.2	321.9
Fees and other revenues not within the scope of revenue recognition guidance	1.4	1.1	4.3	3.4
Total fees and other revenues	116.5	103.4	349.5	325.3
Premiums and other considerations	2.3	33.8	17.2	74.2
Net investment income (loss)	130.8	245.5	490.3	755.2
Total operating revenues	249.6	382.7	857.0	1,154.7
Operating Segments | Principal Asset Management | Principal International | Latin America
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	87.3	74.7	262.4	238.9
Operating Segments | Principal Asset Management | Principal International | Asia
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	28.0	27.7	83.4	83.5
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)	(0.1)	(0.6)	(0.5)
Operating Segments | Principal Asset Management | Principal International | Management fee revenue
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	113.3	100.1	339.2	314.6
Operating Segments | Principal Asset Management | Principal International | Other fee revenue
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	1.8	2.2	6.0	7.3
Operating Segments | Retirement and Income Solutions
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	141.1	133.8	410.9	419.5
Fees and other revenues not within the scope of revenue recognition guidance	276.8	273.4	833.2	844.7
Total fees and other revenues	417.9	407.2	1,244.1	1,264.2
Premiums and other considerations	561.0	607.3	1,763.0	1,197.6
Net investment income (loss)	672.2	549.3	1,933.8	1,682.8
Total operating revenues	1,651.1	1,563.8	4,940.9	4,144.6
Operating Segments | Retirement and Income Solutions | Administrative service fee revenue
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	137.0	129.9	398.8	408.9
Operating Segments | Retirement and Income Solutions | Deposit account fee revenue
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	2.8	2.6	8.5	7.6
Operating Segments | Retirement and Income Solutions | Other fee revenue
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	0.8	0.9	2.3	2.1
Operating Segments | Retirement and Income Solutions | Commission income
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	0.5	0.4	1.3	0.9
Operating Segments | Corporate
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	44.4	44.8	134.4	130.1
Fees and other revenues not within the scope of revenue recognition guidance	(76.9)	(75.2)	(224.2)	(242.8)
Total fees and other revenues	(32.5)	(30.4)	(89.8)	(112.7)
Premiums and other considerations	(1.4)	(1.2)	(3.9)	(2.9)
Net investment income (loss)	40.6	21.4	142.6	110.7
Total operating revenues	6.7	(10.2)	48.9	(4.9)
Operating Segments | Corporate | Other fee revenue
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	21.3	20.4	62.5	59.1
Operating Segments | Corporate | Commission income
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	94.9	89.5	276.9	280.1
Operating Segments | Corporate | Revenue by type - Eliminations
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	$ (71.8)	$ (65.1)	$ (205.0)	$ (209.1)