Reinsurance - Cost of Reinsurance (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021
Reinsurance
Cost of reinsurance asset	$ 3,710.8		$ 3,710.8		$ 46.5
Cost of reinsurance liability	80.2		80.2		$ 22.1
Cost of reinsurance amortization	$ 15.8	$ (3.5)	$ 59.5	$ (11.1)

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