Schedule II - Condensed Financial Information of Registrant (Parent Only) - Statements of Operations (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenues
Net investment income (loss)									$ 3,890.6	$ 3,998.4	$ 3,629.2
Net realized capital gains (losses)									302.6	(52.8)	(75.4)
Total revenues	$ 3,765.1	$ 3,310.7	$ 3,114.6	$ 4,551.3	$ 4,047.2	$ 4,458.4	$ 3,972.6	$ 3,743.9	14,741.7	16,222.1	14,237.2
Expenses
Other operating costs and expenses									4,646.5	4,503.9	4,136.7
Total expenses	3,173.5	3,035.6	2,616.0	4,223.1	3,675.9	4,112.7	3,522.3	3,217.9	13,048.2	14,528.8	12,452.8
Loss before income taxes									1,693.5	1,693.3	1,784.4
Income taxes (benefits)									265.0	249.2	230.7
Net income (loss) attributable to Principal Financial Group, Inc.	$ 472.6	$ 236.0	$ 398.3	$ 288.9	$ 300.9	$ 277.1	$ 386.3	$ 429.9	1,395.8	1,394.2	1,546.5
Principal Financial Group, Inc. parent only | Legal Entities
Revenues
Net investment income (loss)									13.3	19.4	25.8
Net realized capital gains (losses)									7.0	12.3	(8.2)
Total revenues									20.3	31.7	17.6
Expenses
Other operating costs and expenses									200.0	210.9	191.9
Total expenses									200.0	210.9	191.9
Loss before income taxes									(179.7)	(179.2)	(174.3)
Income taxes (benefits)									(46.1)	(44.2)	(62.5)
Equity in the net income (loss) of subsidiaries									1,529.4	1,529.2	1,658.3
Net income (loss) attributable to Principal Financial Group, Inc.									$ 1,395.8	$ 1,394.2	$ 1,546.5