Reinsurance - Cost of Reinsurance (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021	Dec. 31, 2021
Reinsurance
Cost of reinsurance asset	$ 3,727.6		$ 3,727.6		$ 46.5
Cost of reinsurance liability	81.6		81.6		$ 22.1
Cost of reinsurance amortization	$ 49.5	$ (4.3)	$ 43.7	$ (7.6)

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