Segment Information - Depreciation and Amortization Expense by Segment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Segment Information: Depreciation and amortization expense
Total segment depreciation and amortization expense included in pre-tax operating earnings	$ 202.9	$ 208.0	$ 186.6
Depreciation and amortization expense related to exited business	27.1
Depreciation and amortization expense	230.0	208.0	186.6
Retirement and Income Solutions
Segment Information: Depreciation and amortization expense
Depreciation and amortization expense	86.2	81.7	69.1
Principal Global Investors
Segment Information: Depreciation and amortization expense
Depreciation and amortization expense	20.7	21.1	21.6
Principal International
Segment Information: Depreciation and amortization expense
Depreciation and amortization expense	53.9	57.3	56.0
U.S. Insurance Solutions
Segment Information: Depreciation and amortization expense
Depreciation and amortization expense	23.7	24.2	25.1
Corporate
Segment Information: Depreciation and amortization expense
Depreciation and amortization expense	$ 18.4	$ 23.7	$ 14.8