Nature of Operations and Significant Accounting Policies - Recent Accounting Pronouncements and Separate Accounts (Details) - USD ($) $ in Millions	Sep. 30, 2022	Dec. 31, 2021
Recent Accounting Pronouncements
Total stockholders' equity	$ 9,446.2	$ 16,069.4
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	89.7	$ 95.1
Accounting Standards Update 2018-12 - Targeted improvements to the accounting for long-duration insurance contracts | Adjustment related to adoption of ASU | Minimum
Recent Accounting Pronouncements
Total stockholders' equity	(5,000.0)
Accounting Standards Update 2018-12 - Targeted improvements to the accounting for long-duration insurance contracts | Adjustment related to adoption of ASU | Maximum
Recent Accounting Pronouncements
Total stockholders' equity	$ (5,600.0)