Nature of Operations and Significant Accounting Policies (Details) - USD ($) $ in Millions	Sep. 01, 2015	Sep. 30, 2015	Dec. 31, 2014
Separate Accounts
Separate account that primarily includes shares of Principal Financial Group, Inc. stock that were allocated and issued to eligible participants of qualified employee benefit plans as part of the 2001 demutualization		$ 173.3	$ 205.4
AXA pension business
Goodwill and Other Intangible Assets
Purchase price of acquired business	$ 335.5
Distribution agreements | AXA pension business
Goodwill and Other Intangible Assets
Exclusive distribution agreement period	15 years