Future Policy Benefits and Claims - Gross Premiums or Assessments and Interest Accretion (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Future Policy Benefits and Claims
Gross premiums or assessments	$ 1,079.2	$ 579.3
Interest accretion	490.5	508.3
Retirement and Income Solutions
Future Policy Benefits and Claims
Gross premiums or assessments	585.0	123.3
Interest accretion	300.9	291.2
Retirement and Income Solutions | Pension risk transfer
Future Policy Benefits and Claims
Gross premiums or assessments	577.0	116.5
Interest accretion	245.2	232.7
Retirement and Income Solutions | Individual fixed income annuities
Future Policy Benefits and Claims
Gross premiums or assessments	8.0	6.8
Interest accretion	55.7	58.5
Principal Asset Management | Principal International | Latin America | Individual fixed income annuities
Future Policy Benefits and Claims
Gross premiums or assessments	6.6	10.5
Interest accretion	106.2	139.1
Benefits and Protection
Future Policy Benefits and Claims
Gross premiums or assessments	486.1	444.1
Interest accretion	80.9	75.6
Benefits and Protection | Specialty Benefits | Individual disability
Future Policy Benefits and Claims
Gross premiums or assessments	150.6	144.4
Interest accretion	23.2	22.3
Benefits and Protection | Life Insurance | Universal life
Future Policy Benefits and Claims
Gross premiums or assessments	174.6	142.5
Interest accretion	46.3	42.5
Benefits and Protection | Life Insurance | Term life
Future Policy Benefits and Claims
Gross premiums or assessments	160.9	157.2
Interest accretion	11.4	10.8
Corporate | Long-term care insurance
Future Policy Benefits and Claims
Gross premiums or assessments	1.5	1.4
Interest accretion	$ 2.5	$ 2.4