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Market Risk Benefits - Asset and Liability Position and Reconciliation (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Market Risk Benefits
Market risk benefit asset	$ 153.4	$ 109.2
Market risk benefit liability	133.2	207.4
Net asset (liability)	20.2	(98.2)
Retirement and Income Solutions
Market Risk Benefits
Market risk benefit asset	153.4	109.2
Market risk benefit liability	111.9	181.4
Retirement and Income Solutions \| Individual variable annuities
Market Risk Benefits
Market risk benefit asset	153.4	109.2
Market risk benefit liability	111.9	181.4
Net asset (liability)	41.5	(72.2)	$ (494.7)	$ 591.3
Principal Asset Management
Market Risk Benefits
Market risk benefit liability	21.3	26.0
Principal Asset Management \| Principal International \| Guaranteed pension \| Asia
Market Risk Benefits
Market risk benefit liability	21.3	26.0
Net asset (liability)	$ (21.3)	$ (26.0)	$ (35.1)	$ 53.3