Condensed Consolidating Financial Information - Shelf Registration Guarantor, Statements of Operations (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenues
Premiums and other considerations	$ 1,184.3	$ 2,274.2	$ 4,628.4	$ 5,932.0
Fees and other revenues	1,143.0	1,230.0	3,332.6	3,210.1
Net investment income (loss)	917.9	996.6	2,846.1	2,994.7
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities		(31.3)		73.3
Net other-than-temporary impairment (losses) recoveries on available-for-sale securities		(4.7)		(31.3)
Other-than-temporary impairment losses on fixed maturities, available-for-sale reclassified to (from) other comprehensive income		(6.4)		(3.9)
Net impairment (losses) recoveries on available-for-sale securities		(11.1)		(35.2)
Net realized capital gains (losses)	65.5	(42.4)	169.5	38.1
Total revenues	3,310.7	4,458.4	10,976.6	12,174.9
Expenses
Benefits, claims and settlement expenses	1,839.8	2,840.1	6,299.8	7,481.3
Dividends to policyholders	29.9	30.3	90.2	90.3
Operating expenses	1,165.9	1,242.3	3,484.7	3,281.3
Total expenses	3,035.6	4,112.7	9,874.7	10,852.9
Income (loss) before income taxes	275.1	345.7	1,101.9	1,322.0
Income taxes (benefits)	39.2	61.1	164.9	193.2
Net income (loss)	235.9	284.6	937.0	1,128.8
Net income attributable to noncontrolling interest	(0.1)	7.5	13.8	35.5
Net income attributable to PFG	236.0	277.1	923.2	1,093.3
Net income (loss)	235.9	284.6	937.0	1,128.8
Other comprehensive income	306.4	656.3	708.2	2,875.3
Comprehensive income (loss)	$ 542.3	$ 940.9	1,645.2	4,004.1
Principal Financial Group, Inc. parent only | Legal Entities
Revenues
Net investment income (loss)			9.9	14.3
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities				11.6
Net realized capital gains (losses)			5.0	11.6
Total revenues			14.9	25.9
Expenses
Operating expenses			148.4	160.2
Total expenses			148.4	160.2
Income (loss) before income taxes			(133.5)	(134.3)
Income taxes (benefits)			(34.8)	(33.2)
Equity in the net income (loss) of subsidiaries			1,021.9	1,194.4
Net income (loss)			923.2	1,093.3
Net income attributable to PFG			923.2	1,093.3
Net income (loss)			923.2	1,093.3
Other comprehensive income			619.7	2,833.4
Comprehensive income (loss)			1,542.9	3,926.7
Principal Financial Services, Inc. only | Legal Entities
Revenues
Fees and other revenues			261.9	104.3
Net investment income (loss)			(1.4)	(5.6)
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities				16.0
Net realized capital gains (losses)			41.1	16.0
Total revenues			301.6	114.7
Expenses
Operating expenses			403.0	205.5
Total expenses			403.0	205.5
Income (loss) before income taxes			(101.4)	(90.8)
Income taxes (benefits)			(30.6)	(15.2)
Equity in the net income (loss) of subsidiaries			1,084.2	1,264.3
Net income (loss)			1,013.4	1,188.7
Net income attributable to PFG			1,013.4	1,188.7
Net income (loss)			1,013.4	1,188.7
Other comprehensive income			582.4	2,749.2
Comprehensive income (loss)			1,595.8	3,937.9
Principal Life Insurance Company and other subsidiaries combined | Legal Entities
Revenues
Premiums and other considerations			4,628.4	5,932.0
Fees and other revenues			3,079.7	3,114.5
Net investment income (loss)			2,828.1	2,979.2
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities				45.7
Net other-than-temporary impairment (losses) recoveries on available-for-sale securities				(31.3)
Other-than-temporary impairment losses on fixed maturities, available-for-sale reclassified to (from) other comprehensive income				(3.9)
Net impairment (losses) recoveries on available-for-sale securities				(35.2)
Net realized capital gains (losses)			123.3	10.5
Total revenues			10,659.5	12,036.2
Expenses
Benefits, claims and settlement expenses			6,299.8	7,481.3
Dividends to policyholders			90.2	90.3
Operating expenses			2,941.2	2,923.2
Total expenses			9,331.2	10,494.8
Income (loss) before income taxes			1,328.3	1,541.4
Income taxes (benefits)			230.3	241.6
Net income (loss)			1,098.0	1,299.8
Net income attributable to noncontrolling interest			13.8	35.5
Net income attributable to PFG			1,084.2	1,264.3
Net income (loss)			1,098.0	1,299.8
Other comprehensive income			658.3	2,797.6
Comprehensive income (loss)			1,756.3	4,097.4
Eliminations, Shelf Registration Debt Guarantor | Eliminations
Revenues
Fees and other revenues			(9.0)	(8.7)
Net investment income (loss)			9.5	6.8
Net realized capital gains (losses)			0.1
Total revenues			0.6	(1.9)
Expenses
Operating expenses			(7.9)	(7.6)
Total expenses			(7.9)	(7.6)
Income (loss) before income taxes			8.5	5.7
Equity in the net income (loss) of subsidiaries			(2,106.1)	(2,458.7)
Net income (loss)			(2,097.6)	(2,453.0)
Net income attributable to PFG			(2,097.6)	(2,453.0)
Net income (loss)			(2,097.6)	(2,453.0)
Other comprehensive income			(1,152.2)	(5,504.9)
Comprehensive income (loss)			$ (3,249.8)	$ (7,957.9)