Reinsurance - Cost of Reinsurance (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Reinsurance
Cost of reinsurance asset	$ 3,286.6		$ 3,286.6		$ 3,339.1
Cost of reinsurance liability	150.2		150.2		$ 191.1
Cost of reinsurance amortization	$ (25.0)	$ 7.6	$ 8.2	$ 2.6

The reinsurance liability related to the amount of expected net reinsurance costs or profits to be spread over the expected term of the contracts.

No definition available.

Name:	pfg_CostOfReinsuranceLiability
Namespace Prefix:	pfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant