Future Policy Benefits and Claims - Gross Premiums or Assessments and Interest Accretion (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Future Policy Benefits and Claims
Gross premiums or assessments	$ 1,064.0	$ 1,127.6	$ 3,260.1	$ 2,636.4
Interest accretion	460.7	542.3	1,455.1	1,628.6
Retirement and Income Solutions
Future Policy Benefits and Claims
Gross premiums or assessments	565.5	609.7	1,773.4	1,206.8
Interest accretion	308.9	290.8	914.8	871.0
Retirement and Income Solutions | Pension risk transfer
Future Policy Benefits and Claims
Gross premiums or assessments	553.9	603.4	1,741.8	1,186.2
Interest accretion	254.4	233.7	749.5	697.6
Retirement and Income Solutions | Individual fixed income annuities
Future Policy Benefits and Claims
Gross premiums or assessments	11.6	6.3	31.6	20.6
Interest accretion	54.5	57.1	165.3	173.4
Principal Asset Management | Principal International | Latin America | Individual fixed income annuities
Future Policy Benefits and Claims
Gross premiums or assessments	2.4	34.2	17.6	75.2
Interest accretion	56.7	172.7	276.4	523.2
Benefits and Protection
Future Policy Benefits and Claims
Gross premiums or assessments	494.9	482.4	1,465.2	1,350.4
Interest accretion	92.8	76.3	256.5	227.1
Benefits and Protection | Specialty Benefits | Individual disability
Future Policy Benefits and Claims
Gross premiums or assessments	161.9	155.5	467.2	448.4
Interest accretion	23.8	22.5	70.5	67.5
Benefits and Protection | Life Insurance | Universal life
Future Policy Benefits and Claims
Gross premiums or assessments	170.7	168.3	512.8	429.0
Interest accretion	56.7	42.8	150.6	127.1
Benefits and Protection | Life Insurance | Term life
Future Policy Benefits and Claims
Gross premiums or assessments	162.3	158.6	485.2	473.0
Interest accretion	12.3	11.0	35.4	32.5
Corporate | Long-term care insurance
Future Policy Benefits and Claims
Gross premiums or assessments	1.2	1.3	3.9	4.0
Interest accretion	$ 2.3	$ 2.5	$ 7.4	$ 7.3