Schedule II - Condensed Financial Information of Registrant (Parent Only) - Statements of Financial Position (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Assets
Fixed maturities, available-for-sale	$ 78,710.3	$ 70,106.2
Fixed maturities, trading	532.1	675.9
Other investments	5,126.8	4,690.2
Cash and cash equivalents	2,849.8	2,515.9
Deferred income taxes	113.8	123.6
Investment in unconsolidated entities	842.7	830.2
Total assets	296,627.7	276,087.8
Liabilities
Long-term debt	4,279.2	3,734.1
Total liabilities	279,754.8	261,137.1
Stockholders' equity
Common stock, par value $0.01 per share; 2,500 million shares authorized; 481.9 million and 479.3 million shares issued as of 2020 and 2019; 273.3 million and 276.6 million shares outstanding as of 2020 and 2019	4.8	4.8
Additional paid-in capital	10,321.6	10,182.6
Retained earnings (accumulated deficit)	11,838.0	11,074.3
Accumulated other comprehensive income (loss)	2,383.1	1,037.9
Treasury stock, at cost (208.6 million and 202.7 million shares as of 2020 and 2019)	(7,988.6)	(7,681.6)
Total stockholders' equity attributable to Principal Financial Group, Inc.	16,558.9	14,618.0
Total liabilities and stockholders' equity	296,627.7	276,087.8
Principal Financial Group, Inc. parent only | Legal Entities
Assets
Fixed maturities, available-for-sale	813.2	265.8
Fixed maturities, trading	178.8	268.2
Other investments	63.7	10.4
Cash and cash equivalents	302.4	394.9
Income taxes receivable	7.4	11.1
Deferred income taxes	371.2	344.4
Amounts receivable from subsidiaries	4.7	3.8
Other assets	27.1	25.5
Investment in unconsolidated entities	19,714.3	17,539.6
Total assets	21,482.8	18,863.7
Liabilities
Long-term debt	4,223.3	3,625.5
Accrued investment payable	25.3	25.4
Pension liability	668.9	590.6
Other liabilities	6.4	4.2
Total liabilities	4,923.9	4,245.7
Stockholders' equity
Common stock, par value $0.01 per share; 2,500 million shares authorized; 481.9 million and 479.3 million shares issued as of 2020 and 2019; 273.3 million and 276.6 million shares outstanding as of 2020 and 2019	4.8	4.8
Additional paid-in capital	10,321.6	10,182.6
Retained earnings (accumulated deficit)	11,838.0	11,074.3
Accumulated other comprehensive income (loss)	2,383.1	1,037.9
Treasury stock, at cost (208.6 million and 202.7 million shares as of 2020 and 2019)	(7,988.6)	(7,681.6)
Total stockholders' equity attributable to Principal Financial Group, Inc.	16,558.9	14,618.0
Total liabilities and stockholders' equity	$ 21,482.8	$ 18,863.7