Revenues from Contracts with Customers - Disaggregation within Segments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Revenues from Contracts with Customers - Disaggregation of Revenues
Total fees and other revenues	$ 4,095.9	$ 4,137.8	$ 5,041.3
Premiums and other considerations	6,470.9	5,339.7	4,841.5
Net investment income (loss)	4,091.9	3,838.5	4,429.6
Benefits and Protection
Revenues from Contracts with Customers - Disaggregation of Revenues
Premiums and other considerations	3,521.4	3,306.5	2,830.4
Net investment income (loss)	549.5	564.2	917.1
Principal Asset Management
Revenues from Contracts with Customers - Disaggregation of Revenues
Premiums and other considerations	29.0	77.7	127.5
Net investment income (loss)	628.6	840.6	659.1
Retirement and Income Solutions
Revenues from Contracts with Customers - Disaggregation of Revenues
Premiums and other considerations	2,935.0	1,959.7	1,883.6
Net investment income (loss)	2,674.3	2,252.2	2,674.4
Corporate
Revenues from Contracts with Customers - Disaggregation of Revenues
Premiums and other considerations	(14.5)	(4.2)
Net investment income (loss)	239.5	181.5	179.0
Operating Segments
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	2,814.9	2,875.8	3,150.1
Total operating revenues	14,660.2	13,400.4	14,442.7
Operating Segments | Benefits and Protection
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	89.8	80.1	75.3
Total operating revenues	4,551.3	4,302.8	4,792.4
Operating Segments | Benefits and Protection | Specialty Benefits
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	15.9	15.1	14.9
Fees and other revenues not within the scope of revenue recognition guidance	18.2	18.6	19.0
Total fees and other revenues	34.1	33.7	33.9
Premiums and other considerations	3,020.9	2,771.1	2,496.4
Net investment income (loss)	174.4	179.8	179.3
Total operating revenues	3,229.4	2,984.6	2,709.6
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	15.9	15.1	14.9
Operating Segments | Benefits and Protection | Life Insurance
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	74.0	65.1	60.6
Fees and other revenues not within the scope of revenue recognition guidance	333.3	321.5	885.0
Total fees and other revenues	407.3	386.6	945.6
Premiums and other considerations	514.9	535.9	334.0
Net investment income (loss)	401.5	396.3	803.4
Total operating revenues	1,323.7	1,318.8	2,083.0
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	31.2	27.6	26.7
Operating Segments | Benefits and Protection | Life Insurance | Commission income
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	42.8	37.5	33.9
Operating Segments | Principal Asset Management
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	1,989.6	2,077.6	2,254.6
Total operating revenues	2,782.3	3,181.3	3,193.0
Operating Segments | Principal Asset Management | Principal Global Investors
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	1,554.1	1,675.0	1,787.9
Fees and other revenues not within the scope of revenue recognition guidance	24.9	27.4	36.2
Total fees and other revenues	1,579.0	1,702.4	1,824.1
Net investment income (loss)	32.2	13.1	3.9
Total operating revenues	1,611.2	1,715.5	1,828.0
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	1,372.0	1,434.6	1,514.1
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	182.1	240.4	273.8
Operating Segments | Principal Asset Management | Principal International
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	456.5	426.3	492.7
Fees and other revenues not within the scope of revenue recognition guidance	5.8	4.5	4.2
Total fees and other revenues	462.3	430.8	496.9
Premiums and other considerations	29.0	77.7	127.5
Net investment income (loss)	701.5	980.9	766.7
Total operating revenues	1,192.8	1,489.4	1,391.1
Operating Segments | Principal Asset Management | Principal International | Latin America
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	346.9	315.2	364.0
Operating Segments | Principal Asset Management | Principal International | Asia
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	110.4	111.5	129.6
Operating Segments | Principal Asset Management | Principal International | Geographical Eliminations
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	(0.8)	(0.4)	(0.9)
Operating Segments | Principal Asset Management | Principal International | Management fee revenue
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	448.1	417.1	484.4
Operating Segments | Principal Asset Management | Principal International | Other fee revenue
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	8.4	9.2	8.3
Operating Segments | Retirement and Income Solutions
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	556.3	551.4	590.1
Fees and other revenues not within the scope of revenue recognition guidance	1,118.7	1,114.0	1,226.9
Total fees and other revenues	1,675.0	1,665.4	1,817.0
Premiums and other considerations	2,935.0	1,959.7	1,883.6
Net investment income (loss)	2,640.2	2,274.1	2,728.8
Total operating revenues	7,250.2	5,899.2	6,429.4
Operating Segments | Retirement and Income Solutions | Administrative service fee revenue
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	539.5	537.0	576.7
Operating Segments | Retirement and Income Solutions | Deposit account fee revenue
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	11.3	10.2	9.2
Operating Segments | Retirement and Income Solutions | Other fee revenue
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	3.6	3.0	3.5
Operating Segments | Retirement and Income Solutions | Commission income
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	1.9	1.2	0.7
Operating Segments | Corporate
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	179.2	166.7	230.1
Fees and other revenues not within the scope of revenue recognition guidance	(299.0)	(312.6)	(359.3)
Total fees and other revenues	(119.8)	(145.9)	(129.2)
Premiums and other considerations	(14.5)	(4.2)
Net investment income (loss)	210.7	167.2	157.1
Total operating revenues	76.4	17.1	27.9
Operating Segments | Corporate | Other fee revenue
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	84.1	79.7	68.8
Operating Segments | Corporate | Commission income
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	373.9	366.2	388.9
Operating Segments | Corporate | Revenue by type - Eliminations
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	$ (278.8)	$ (279.2)	$ (227.6)