Insurance Liabilities (Details 2)			12 Months Ended
	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2014 Principal Life Insurance Company item	Dec. 31, 2014 Principal Life Insurance Company 1998 Funding agreement program USD ($)	Dec. 31, 2013 Principal Life Insurance Company 1998 Funding agreement program USD ($)	Dec. 31, 1998 Principal Life Insurance Company 1998 Funding agreement program USD ($)	Dec. 31, 2014 Principal Life Insurance Company 2001 Funding agreement program USD ($)	Dec. 31, 2013 Principal Life Insurance Company 2001 Funding agreement program USD ($)	Dec. 31, 2001 Principal Life Insurance Company 2001 Funding agreement program USD ($)	Dec. 31, 2014 Principal Life Insurance Company 2004 Funding agreement program USD ($)	Dec. 31, 2013 Principal Life Insurance Company 2004 Funding agreement program USD ($)	Nov. 30, 2007 Principal Life Insurance Company 2004 Funding agreement program USD ($)	Feb. 28, 2006 Principal Life Insurance Company 2004 Funding agreement program USD ($)	Mar. 31, 2004 Principal Life Insurance Company 2004 Funding agreement program USD ($)	Dec. 31, 2014 Principal Life Insurance Company 2006 Funding agreement program USD ($)	Dec. 31, 2013 Principal Life Insurance Company 2006 Funding agreement program USD ($)	Dec. 31, 2006 Principal Life Insurance Company 2006 Funding agreement program USD ($)	Dec. 31, 2006 Principal Life Insurance Company 2006 Funding agreement program EUR (€)	Dec. 31, 2014 Principal Life Insurance Company 2011 Funding agreement program USD ($)	Dec. 31, 2013 Principal Life Insurance Company 2011 Funding agreement program USD ($)	Dec. 31, 2011 Principal Life Insurance Company 2011 Funding agreement program USD ($)
Funding agreement disclosures
Number of separate funding agreement programs			5
Number of funding agreement programs not guaranteed by PFG			3
Maximum authorized amount of funding agreements to be issued						$ 4,000,000,000			$ 7,000,000,000					$ 4,000,000,000			$ 5,300,000,000	€ 4,000,000,000			$ 5,000,000,000
Funding agreements	7,338,100,000	7,642,900,000		111,200,000	370,900,000		505,800,000	637,600,000		549,200,000	975,000,000				1,137,100,000	1,278,700,000			3,284,700,000	2,630,500,000
Additional maximum authorized amount of funding agreements to be issued												5,000,000,000	5,000,000,000
Amount of funding agreement authorization used at time additional amount authorized												$ 9,000,000,000	$ 4,000,000,000