Stockholders' Equity - AOCI and Noncontrolling Interest (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2022	Mar. 31, 2021
Change in accumulated other comprehensive income (loss) rollforward
Balances		$ 16,069.4
Purchase of subsidiary shares from noncontrolling interest	[1]	(6.7)	$ (16.6)
Balances		11,897.6
Change in redeemable noncontrolling interest rollforward
Redeemable noncontrolling interest, balance at beginning of period		332.5	255.6
Net income (loss) attributable to redeemable noncontrolling interest		(10.3)	(1.8)
Contributions from redeemable noncontrolling interest		24.0	17.8
Distributions to redeemable noncontrolling interest		(39.6)	(16.3)
Change in redemption value of redeemable noncontrolling interest		0.1	8.2
Other comprehensive income (loss) attributable to redeemable noncontrolling interest		0.1
Redeemable noncontrolling interest, balance at end of period		306.8	263.5
Accumulated other comprehensive income (loss)
Change in accumulated other comprehensive income (loss) rollforward
Balances		1,610.9	2,383.1
Other comprehensive income (loss) during the period, net of adjustments		(3,497.4)	(1,413.6)
Amounts reclassified to accumulated other comprehensive income (loss)		(34.1)	(15.7)
Other comprehensive income (loss) attributable to Principal Financial Group, Inc.		(3,531.5)	(1,429.3)
Balances		(1,920.6)	953.8
Net unrealized gains (losses) on available-for-sale securities
Change in accumulated other comprehensive income (loss) rollforward
Balances		3,467.4	4,138.3
Other comprehensive income (loss) during the period, net of adjustments		(3,638.5)	(1,351.7)
Amounts reclassified to accumulated other comprehensive income (loss)		(35.4)	(21.7)
Other comprehensive income (loss) attributable to Principal Financial Group, Inc.		(3,673.9)	(1,373.4)
Balances		(206.5)	2,764.9
Net unrealized gains (losses) on available-for-sale debt securities with allowance for credit losses		6.2	(2.4)
Net unrealized gains (losses) on derivative instruments
Change in accumulated other comprehensive income (loss) rollforward
Balances		51.8	18.2
Other comprehensive income (loss) during the period, net of adjustments		(10.9)	1.3
Amounts reclassified to accumulated other comprehensive income (loss)		(5.4)	(3.5)
Other comprehensive income (loss) attributable to Principal Financial Group, Inc.		(16.3)	(2.2)
Balances		35.5	16.0
Foreign currency translation adjustment
Change in accumulated other comprehensive income (loss) rollforward
Balances		(1,563.6)	(1,312.9)
Other comprehensive income (loss) during the period, net of adjustments		152.0	(56.0)
Amounts reclassified to accumulated other comprehensive income (loss)		0.0
Other comprehensive income (loss) attributable to Principal Financial Group, Inc.		152.0	(56.0)
Balances		(1,411.6)	(1,368.9)
Unrecognized postretirement benefit obligations
Change in accumulated other comprehensive income (loss) rollforward
Balances		(344.7)	(460.5)
Other comprehensive income (loss) during the period, net of adjustments			(7.2)
Amounts reclassified to accumulated other comprehensive income (loss)		6.7	9.5
Other comprehensive income (loss) attributable to Principal Financial Group, Inc.		6.7	2.3
Balances		$ (338.0)	$ (458.2)

[1] Excludes amounts attributable to redeemable noncontrolling interest. See Note 9, Stockholders’ Equity, for further details.