Nature of Operations and Significant Accounting Policies - Balances and changes in MRBs (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Balances and changes in MRBs
Balance at beginning of period	$ (98.2)
Balance at end of period	(87.1)	$ (98.2)
Individual variable annuities | Retirement and Income Solutions
Balances and changes in MRBs
Balance at beginning of period	(72.2)	(494.7)	$ (591.3)
Effect of changes in nonperformance risk	31.7	(109.5)	(106.7)
Adjusted balance at beginning of period	(103.9)	(385.2)	(484.6)
Interest accrual and expected policyholder behavior	(19.8)	(90.1)	(120.7)
Benefit payments	0.2	1.3	0.4
Changes in interest rates	(54.2)	539.1	154.3
Changes in equity markets	46.4	(112.4)	106.4
Changes in equity index volatility	30.6	(50.2)	15.1
Actual policyholder behavior different from expected behavior	(2.0)	1.5	2.3
Changes in future expected policyholder behavior	0.0	(6.1)	(96.6)
Changes in other future expected assumptions	0.0	(1.8)	38.2
Adjusted balance at end of period	(102.7)	(103.9)	(385.2)
Effect of changes in nonperformance risk at end of period	39.6	31.7	(109.5)
Balance at end of period	(63.1)	(72.2)	(494.7)
Guaranteed pension | Principal Asset Management | Principal International | Asia
Balances and changes in MRBs
Balance at beginning of period	(26.0)	(35.1)	(53.3)
Effect of changes in nonperformance risk	(1.2)	(4.3)	6.5
Adjusted balance at beginning of period	(24.8)	(30.8)	(46.8)
Interest accrual and expected policyholder behavior	(2.8)	(7.1)	(5.3)
Benefit payments	3.7	9.5	5.7
Changes in interest rates	0.7	3.9	7.6
Changes in equity markets	0.1	(1.0)	1.4
Actual policyholder behavior different from expected behavior	0.4	0.7	3.6
Changes in future expected policyholder behavior			0.5
Changes in other future expected assumptions			2.3
Foreign currency translation adjustment			0.2
Adjusted balance at end of period	(22.6)	(24.8)	(30.8)
Effect of changes in nonperformance risk at end of period	(1.4)	(1.2)	(4.3)
Balance at end of period	$ (24.0)	$ (26.0)	$ (35.1)