Revenues from Contracts with Customers - Disaggregation within Segments (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	$ 947.6	$ 1,265.3	$ 2,162.6	$ 2,459.2
Premiums and other considerations	1,366.2	1,269.7	2,253.6	2,104.8
Net investment income (loss)	816.5	1,045.5	1,934.6	2,073.6
Operating Segments
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	749.6	795.2	1,501.3	1,533.3
Total operating revenues	3,141.2	3,613.8	6,415.1	6,727.3
Operating Segments | Retirement and Income Solutions
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	141.3	150.1	285.7	294.4
Total operating revenues	1,336.9	1,670.9	2,619.9	2,894.9
Operating Segments | Retirement and Income Solutions | Retirement and Income Solutions - Fee
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	138.5	147.7	280.2	289.6
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	429.4	474.2	889.4	929.8
Premiums and other considerations				0.5
Net investment income (loss)	134.1	105.7	252.9	212.7
Total operating revenues	563.5	579.9	1,142.3	1,143.0
Operating Segments | Retirement and Income Solutions | Retirement and Income Solutions - Fee | Administrative service fee revenue
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	137.5	145.4	279.0	287.2
Operating Segments | Retirement and Income Solutions | Retirement and Income Solutions - Fee | Other fee revenue
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	1.0	2.3	1.2	2.4
Operating Segments | Retirement and Income Solutions | Retirement and Income Solutions - Spread
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	2.8	2.4	5.5	4.8
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	2.9	5.1	6.7	9.5
Premiums and other considerations	467.0	525.0	590.3	629.8
Net investment income (loss)	303.5	560.9	880.6	1,112.6
Total operating revenues	773.4	1,091.0	1,477.6	1,751.9
Operating Segments | Retirement and Income Solutions | Retirement and Income Solutions - Spread | Deposit account fee revenue
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	2.5	2.2	5.0	4.5
Operating Segments | Retirement and Income Solutions | Retirement and Income Solutions - Spread | Commission income
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	0.3	0.2	0.5	0.3
Operating Segments | Principal Global Investors
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	451.6	444.0	881.2	850.1
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	460.5	452.1	895.4	866.2
Net investment income (loss)	3.1	1.6	3.5	2.7
Total operating revenues	463.6	453.7	898.9	868.9
Operating Segments | Principal Global Investors | Management fee revenue
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	364.5	374.1	743.5	730.0
Operating Segments | Principal Global Investors | Other fee revenue
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	87.1	69.9	137.7	120.1
Operating Segments | Principal International
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	109.2	126.5	219.6	248.4
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	110.3	127.6	221.9	250.5
Premiums and other considerations	30.1	41.9	40.4	69.2
Net investment income (loss)	298.7	136.7	491.7	294.5
Total operating revenues	439.1	306.2	754.0	614.2
Operating Segments | Principal International | Latin America
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	81.7	92.7	163.7	181.8
Operating Segments | Principal International | Asia
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	27.3	33.5	55.6	65.8
Operating Segments | Principal International | Principal International Corporate / Regional Office
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	0.5	0.7	0.9	1.5
Operating Segments | Principal International | Geographical Eliminations
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	(0.3)	(0.4)	(0.6)	(0.7)
Operating Segments | Principal International | Management fee revenue
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	106.8	124.7	214.5	244.8
Operating Segments | Principal International | Other fee revenue
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	2.4	1.8	5.1	3.6
Operating Segments | U.S. Insurance Solutions
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	19.8	18.7	39.2	36.1
Total operating revenues	908.6	1,181.9	2,149.6	2,356.8
Operating Segments | U.S. Insurance Solutions | Specialty Benefits insurance
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	3.7	3.8	7.7	7.5
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	8.2	8.5	16.9	17.0
Premiums and other considerations	686.8	616.8	1,352.4	1,222.1
Net investment income (loss)	56.6	42.6	100.0	84.4
Total operating revenues	751.6	667.9	1,469.3	1,323.5
Operating Segments | U.S. Insurance Solutions | Specialty Benefits insurance | Administrative service fee revenue
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	3.7	3.8	7.7	7.5
Operating Segments | U.S. Insurance Solutions | Individual Life insurance
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	16.2	15.0	31.6	28.7
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	(47.8)	226.5	193.6	460.4
Premiums and other considerations	183.6	86.0	272.4	183.2
Net investment income (loss)	21.4	201.6	214.6	389.8
Total operating revenues	157.2	514.1	680.6	1,033.4
Operating Segments | U.S. Insurance Solutions | Individual Life insurance | Administrative service fee revenue
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	7.1	6.6	13.9	12.5
Operating Segments | U.S. Insurance Solutions | Individual Life insurance | Commission income
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	9.1	8.4	17.7	16.2
Operating Segments | Corporate
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	27.7	55.9	75.6	104.3
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	(51.7)	(32.6)	(95.2)	(70.2)
Premiums and other considerations	(1.2)		(1.7)
Net investment income (loss)	45.9	33.7	89.6	62.7
Total operating revenues	(7.0)	1.1	(7.3)	(7.5)
Operating Segments | Corporate | Other fee revenue
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	18.9	17.4	38.7	33.7
Operating Segments | Corporate | Commission income
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	93.4	95.7	190.6	187.7
Operating Segments | Corporate | Revenue by type - Eliminations
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	$ (84.6)	$ (57.2)	$ (153.7)	$ (117.1)