Future Policy Benefits and Claims - Gross Premiums or Assessments and Interest Accretion (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Future Policy Benefits and Claims
Gross premiums or assessments	$ 1,268.8	$ 1,079.2
Interest accretion	497.4	490.5
Retirement and Income Solutions
Future Policy Benefits and Claims
Gross premiums or assessments	770.0	585.0
Interest accretion	326.1	300.9
Retirement and Income Solutions | Pension risk transfer
Future Policy Benefits and Claims
Gross premiums or assessments	753.0	577.0
Interest accretion	272.9	245.2
Retirement and Income Solutions | Individual fixed income annuities
Future Policy Benefits and Claims
Gross premiums or assessments	17.0	8.0
Interest accretion	53.2	55.7
Principal Asset Management | Principal International | Latin America | Individual fixed income annuities
Future Policy Benefits and Claims
Gross premiums or assessments	2.1	6.6
Interest accretion	71.1	106.2
Benefits and Protection
Future Policy Benefits and Claims
Gross premiums or assessments	495.2	486.1
Interest accretion	98.0	80.9
Benefits and Protection | Specialty Benefits | Individual disability
Future Policy Benefits and Claims
Gross premiums or assessments	154.9	150.6
Interest accretion	24.4	23.2
Benefits and Protection | Life Insurance | Universal life
Future Policy Benefits and Claims
Gross premiums or assessments	176.2	174.6
Interest accretion	60.4	46.3
Benefits and Protection | Life Insurance | Term life
Future Policy Benefits and Claims
Gross premiums or assessments	164.1	160.9
Interest accretion	13.2	11.4
Corporate | Long-term care insurance
Future Policy Benefits and Claims
Gross premiums or assessments	1.5	1.5
Interest accretion	$ 2.2	$ 2.5