Revenues from Contracts with Customers - Disaggregation within Segments (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Revenues from Contracts with Customers - Disaggregation of Revenues
Total fees and other revenues	$ 1,015.7	$ 1,251.8	$ 3,178.3	$ 3,711.0
Premiums and other considerations	1,486.5	1,230.5	3,740.1	3,335.3
Net investment income (loss)	908.2	1,093.4	2,842.8	3,167.0
Operating Segments
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	692.9	796.5	2,194.2	2,329.8
Total operating revenues	3,442.5	3,622.0	9,857.6	10,349.3
Operating Segments | Retirement and Income Solutions
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	133.8	146.6	419.5	441.0
Total operating revenues	1,582.6	1,652.9	4,202.5	4,547.8
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	130.8	144.2	411.0	433.8
Fees and other revenues not within the scope of revenue recognition guidance	291.3	324.1	900.5	964.3
Total fees and other revenues	422.1	468.3	1,311.5	1,398.1
Premiums and other considerations				0.5
Net investment income (loss)	129.4	112.6	382.3	325.3
Total operating revenues	551.5	580.9	1,693.8	1,723.9
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	129.9	144.2	408.9	431.4
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	0.9		2.1	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	3.0	2.4	8.5	7.2
Fees and other revenues not within the scope of revenue recognition guidance	0.9	2.1	2.1	6.8
Total fees and other revenues	3.9	4.5	10.6	14.0
Premiums and other considerations	607.3	482.1	1,197.6	1,111.9
Net investment income (loss)	419.9	585.4	1,300.5	1,698.0
Total operating revenues	1,031.1	1,072.0	2,508.7	2,823.9
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	2.6	2.2	7.6	6.7
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	0.4	0.2	0.9	0.5
Operating Segments | Principal Global Investors
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	395.8	453.5	1,277.0	1,303.6
Fees and other revenues not within the scope of revenue recognition guidance	6.4	11.0	20.6	27.1
Total fees and other revenues	402.2	464.5	1,297.6	1,330.7
Net investment income (loss)	3.8	0.7	7.3	3.4
Total operating revenues	406.0	465.2	1,304.9	1,334.1
Operating Segments | Principal Global Investors | Management fee revenue
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	351.7	389.9	1,095.2	1,119.9
Operating Segments | Principal Global Investors | Other fee revenue
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	44.1	63.6	181.8	183.7
Operating Segments | Principal International
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	102.3	125.1	321.9	373.5
Fees and other revenues not within the scope of revenue recognition guidance	1.1	1.0	3.4	3.1
Total fees and other revenues	103.4	126.1	325.3	376.6
Premiums and other considerations	33.8	36.6	74.2	105.8
Net investment income (loss)	239.7	165.4	731.4	459.9
Total operating revenues	376.9	328.1	1,130.9	942.3
Operating Segments | Principal International | Latin America
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	74.6	91.5	238.3	273.3
Operating Segments | Principal International | Asia
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	27.5	33.5	83.1	99.3
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	0.5	1.4	2.0
Operating Segments | Principal International | Geographical Eliminations
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	(0.3)	(0.4)	(0.9)	(1.1)
Operating Segments | Principal International | Management fee revenue
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	100.1	123.0	314.6	367.8
Operating Segments | Principal International | Other fee revenue
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	2.2	2.1	7.3	5.7
Operating Segments | U.S. Insurance Solutions
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	20.7	19.7	59.9	55.8
Total operating revenues	1,092.9	1,190.1	3,242.5	3,546.9
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	3.9	11.4	11.4
Fees and other revenues not within the scope of revenue recognition guidance	4.8	5.4	14.0	14.9
Total fees and other revenues	8.5	9.3	25.4	26.3
Premiums and other considerations	704.0	629.6	2,056.4	1,851.7
Net investment income (loss)	36.5	45.5	136.5	129.9
Total operating revenues	749.0	684.4	2,218.3	2,007.9
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	3.9	11.4	11.4
Operating Segments | U.S. Insurance Solutions | Individual Life insurance
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	17.0	15.8	48.6	44.5
Fees and other revenues not within the scope of revenue recognition guidance	91.3	204.1	253.3	635.8
Total fees and other revenues	108.3	219.9	301.9	680.3
Premiums and other considerations	142.7	82.2	415.1	265.4
Net investment income (loss)	93.0	203.6	307.6	593.4
Total operating revenues	344.0	505.7	1,024.6	1,539.1
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	7.0	6.8	20.9	19.3
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	10.0	9.0	27.7	25.2
Operating Segments | Corporate
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	40.3	51.6	115.9	155.9
Fees and other revenues not within the scope of revenue recognition guidance	(76.6)	(91.8)	(247.4)	(266.3)
Total fees and other revenues	(36.3)	(40.2)	(131.5)	(110.4)
Premiums and other considerations	(1.2)		(2.9)
Net investment income (loss)	21.6	25.9	111.2	88.6
Total operating revenues	(15.9)	(14.3)	(23.2)	(21.8)
Operating Segments | Corporate | Other fee revenue
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	20.4	17.3	59.1	51.0
Operating Segments | Corporate | Commission income
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	89.5	99.8	280.1	287.5
Operating Segments | Corporate | Revenue by type - Eliminations
Revenues from Contracts with Customers - Disaggregation of Revenues
Total revenues from contracts with customers	$ (69.6)	$ (65.5)	$ (223.3)	$ (182.6)