Market Risk Benefits - Net Asset (Liability) Balances and Changes in Valuation of MRBs for Asia - Guaranteed Pension (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Net asset (liability) balances and the changes in the valuation of the MRBs
Balance at beginning of period, market risk benefits	$ (98.2)
Balance at end of period, market risk benefits	60.6	$ (98.2)
Net amount at risk				$ 644.6
Principal Asset Management | Principal International | Guaranteed pension | Asia
Net asset (liability) balances and the changes in the valuation of the MRBs
Balance at beginning of period, market risk benefits	(26.0)	(35.1)	$ (53.3)
Effect of changes in nonperformance risk at beginning of period	1.2	4.3	(6.5)
Adjusted balance at beginning of period, market risk benefits	(24.8)	(30.8)	(46.8)
Interest accrual and expected policyholder behavior	(7.6)	(7.1)	(5.3)
Benefit payments	10.4	9.5	5.7
Changes in interest rates	1.1	3.9	7.6
Changes in equity markets	0.2	(1.0)	1.4
Actual policyholder behavior different from expected behavior	(0.1)	0.7	3.6
Foreign currency translation adjustment	0.1
Adjusted balance at end of period, market risk benefits	(20.7)	(24.8)	(30.8)
Effect of changes in nonperformance risk at end of period	1.0	1.2	4.3
Balance at end of period, market risk benefits	$ (21.7)	$ (26.0)	$ (35.1)
Weighted-average attained age of policyholders (years)	50 years 2 months 12 days	50 years
Net amount at risk	$ 76.1	$ 91.0		$ 53.3