Consolidated Statements of Operations - 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
Premiums and other considerations									$ 6,037.4	$ 7,866.6	$ 6,409.6
Fees and other revenues									4,511.1	4,409.9	4,273.8
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
Benefits, claims and settlement expenses									8,281.5	9,905.8	8,192.5
Dividends to policyholders									120.2	119.1	123.6
Operating 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
Income (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)	491.5	235.9	416.1	285.0	315.3	284.6	392.1	452.1	1,428.5	1,444.1	1,553.7
Net income (loss) attributable to noncontrolling interest									32.7	49.9	7.2
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
Earnings per common share
Basic earnings per common share (in dollars per share)	$ 1.72	$ 0.86	$ 1.45	$ 1.05	$ 1.08	$ 0.99	$ 1.38	$ 1.54	$ 5.08	$ 5.00	$ 5.41
Diluted earnings per common share (in dollars per share)	$ 1.70	$ 0.85	$ 1.45	$ 1.04	$ 1.07	$ 0.98	$ 1.37	$ 1.53	$ 5.05	$ 4.96	$ 5.36