Schedule II - Condensed Financial Information of Registrant (Parent Only) - Statements of Financial Position (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Assets
Fixed maturities, available-for-sale	$ 70,106.2	$ 60,108.5
Fixed maturities, trading	675.9	636.1
Other investments	4,690.2	4,310.3
Cash and cash equivalents	2,515.9	2,977.5
Deferred income tax assets	123.6	141.3
Investment in unconsolidated entities	830.2	868.8
Total assets	276,087.8	243,036.1
Liabilities
Long-term debt	3,734.1	3,259.6
Total liabilities	261,137.1	231,188.9
Stockholders' equity
Common stock, par value $0.01 per share - 2,500.0 million shares authorized, 479.3 million and 476.7 million shares issued, and 276.6 million and 279.5 million shares outstanding in 2019 and 2018	4.8	4.8
Additional paid-in capital	10,182.6	10,060.7
Retained earnings (accumulated deficit)	11,074.3	10,290.2
Accumulated other comprehensive income (loss)	1,037.9	(1,565.1)
Treasury stock, at cost (202.7 million and 197.2 million shares in 2019 and 2018)	(7,681.6)	(7,400.6)
Total stockholders' equity attributable to Principal Financial Group, Inc.	14,618.0	11,390.0
Total liabilities and stockholders' equity	276,087.8	243,036.1
Principal Financial Group, Inc. parent only | Legal Entities
Assets
Fixed maturities, available-for-sale	265.8	211.5
Fixed maturities, trading	268.2	308.9
Other investments	10.4	10.7
Cash and cash equivalents	394.9	334.9
Income taxes receivable	11.1	16.9
Deferred income tax assets	344.4	331.0
Amounts receivable from subsidiaries	3.8	5.2
Other assets	25.5	23.3
Investment in unconsolidated entities	17,539.6	13,862.4
Total assets	18,863.7	15,104.8
Liabilities
Long-term debt	3,625.5	3,129.8
Accrued investment payable	25.4	23.1
Pension liability	590.6	557.9
Other liabilities	4.2	4.0
Total liabilities	4,245.7	3,714.8
Stockholders' equity
Common stock, par value $0.01 per share - 2,500.0 million shares authorized, 479.3 million and 476.7 million shares issued, and 276.6 million and 279.5 million shares outstanding in 2019 and 2018	4.8	4.8
Additional paid-in capital	10,182.6	10,060.7
Retained earnings (accumulated deficit)	11,074.3	10,290.2
Accumulated other comprehensive income (loss)	1,037.9	(1,565.1)
Treasury stock, at cost (202.7 million and 197.2 million shares in 2019 and 2018)	(7,681.6)	(7,400.6)
Total stockholders' equity attributable to Principal Financial Group, Inc.	14,618.0	11,390.0
Total liabilities and stockholders' equity	$ 18,863.7	$ 15,104.8