Segment Information - Reconciliation of Segment Operating Revenues and Earnings to Consolidated (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Operating Revenue And Profit (Loss) From Segments To Consolidated
Total revenues	$ 4,598.7	$ 4,625.3	$ 10,975.0	$ 14,385.3
Pre-tax income (loss) from exited business	879.2	1,178.9	352.3	4,903.4
Income (loss) before income taxes	1,604.9	1,640.4	1,846.0	5,989.4
Retirement and Income Solutions
Operating Revenue And Profit (Loss) From Segments To Consolidated
Inter-segment revenues	101.8	89.9	293.6	275.9
Principal Asset Management
Operating Revenue And Profit (Loss) From Segments To Consolidated
Inter-segment revenues	79.9	69.4	220.5	231.1
Operating Segments
Operating Revenue And Profit (Loss) From Segments To Consolidated
Operating revenues	3,478.0	3,422.4	10,418.1	9,813.5
Pre-tax operating earnings (losses)	581.3	493.3	1,470.1	1,491.0
Operating Segments | Retirement and Income Solutions
Operating Revenue And Profit (Loss) From Segments To Consolidated
Operating revenues	1,651.1	1,563.8	4,940.9	4,144.6
Pre-tax operating earnings (losses)	304.7	206.3	786.8	755.1
Operating Segments | Principal Asset Management
Operating Revenue And Profit (Loss) From Segments To Consolidated
Operating revenues	668.8	783.0	2,048.2	2,441.3
Pre-tax operating earnings (losses)	222.4	206.0	598.4	686.4
Operating Segments | Principal Asset Management | Principal International
Operating Revenue And Profit (Loss) From Segments To Consolidated
Operating revenues	249.6	382.7	857.0	1,154.7
Operating Segments | Principal Asset Management | Principal Global Investors
Operating Revenue And Profit (Loss) From Segments To Consolidated
Operating revenues	424.6	406.0	1,207.4	1,304.9
Operating Segments | Principal Asset Management | Eliminations
Operating Revenue And Profit (Loss) From Segments To Consolidated
Operating revenues	(5.4)	(5.7)	(16.2)	(18.3)
Operating Segments | Benefits and Protection
Operating Revenue And Profit (Loss) From Segments To Consolidated
Operating revenues	1,151.4	1,085.8	3,380.1	3,232.5
Pre-tax operating earnings (losses)	169.0	181.8	393.2	432.2
Operating Segments | Benefits and Protection | Specialty Benefits
Operating Revenue And Profit (Loss) From Segments To Consolidated
Operating revenues	816.6	749.0	2,391.0	2,218.3
Operating Segments | Benefits and Protection | Life Insurance
Operating Revenue And Profit (Loss) From Segments To Consolidated
Operating revenues	335.0	336.9	989.6	1,014.6
Operating Segments | Benefits and Protection | Eliminations
Operating Revenue And Profit (Loss) From Segments To Consolidated
Operating revenues	(0.2)	(0.1)	(0.5)	(0.4)
Operating Segments | Corporate
Operating Revenue And Profit (Loss) From Segments To Consolidated
Operating revenues	6.7	(10.2)	48.9	(4.9)
Pre-tax operating earnings (losses)	(114.8)	(100.8)	(308.3)	(382.7)
Reconciling Items
Operating Revenue And Profit (Loss) From Segments To Consolidated
Net realized capital gains (losses), net of related revenue adjustments	226.2	(21.2)	141.6	(365.9)
Revenues from exited business	924.9	1,249.6	508.2	5,010.8
Adjustments related to equity method investments	(18.5)	(16.9)	(57.9)	(47.7)
Market risk benefit derivative settlements	(11.9)	(8.6)	(35.0)	(25.4)
Pre-tax net realized capital gains (losses), as adjusted	155.5	(16.2)	70.1	(413.6)
Pre-tax income (loss) from exited business	879.2	1,178.9	352.3	4,903.4
Earnings adjustments related to equity method investments and noncontrolling interest	$ (11.1)	$ (15.6)	$ (46.5)	$ 8.6