Insurance Liabilities - Contractholder Funding Agreements (Details) $ in Millions, € in Billions	12 Months Ended
	Dec. 31, 2020 USD ($) item	Apr. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)	Nov. 30, 2017 USD ($)	Jun. 30, 2015 USD ($)	Dec. 31, 2011 USD ($)	Dec. 31, 2006 USD ($)	Dec. 31, 2006 EUR (€)	Mar. 31, 2004 USD ($)	Dec. 31, 2001 USD ($)	Dec. 31, 1998 USD ($)
Funding agreement disclosures
Funding agreements	$ 9,407.3		$ 8,640.6
Principal Life Insurance Company
Funding agreement disclosures
Number of separate funding agreement programs | item	5
Number of funding agreement programs not guaranteed by PFG | item	3
Principal Life Insurance Company | FHLB Des Moines funding agreement program
Funding agreement disclosures
Funding agreements	$ 4,252.5		4,010.9
Principal Life Insurance Company | 1998 Funding agreement program
Funding agreement disclosures
Maximum authorized amount of funding agreements to be issued											$ 4,000.0
Funding agreements	75.0		75.2
Principal Life Insurance Company | 2006 Funding agreement program
Funding agreement disclosures
Maximum authorized amount of funding agreements to be issued							$ 5,300.0	€ 4.0
Funding agreements	122.4		112.2
Principal Life Insurance Company | 2001 Funding agreement program
Funding agreement disclosures
Maximum authorized amount of funding agreements to be issued										$ 7,000.0
Funding agreements	201.8		201.7
Principal Life Insurance Company | 2004 Funding agreement program
Funding agreement disclosures
Maximum authorized amount of funding agreements to be issued									$ 9,000.0
Funding agreements		$ 0.0	26.2
Principal Life Insurance Company | 2011 Funding agreement program
Funding agreement disclosures
Maximum authorized amount of funding agreements to be issued						$ 5,000.0
Funding agreements	$ 4,755.8		$ 4,214.3
Additional maximum authorized amount of funding agreements to be issued				$ 4,000.0	$ 4,000.0
Amount of funding agreement authorization used at time additional amount authorized					$ 5,000.0