v3.26.3
Stockholders' Equity - Other Comprehensive Income (Loss) (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2026
Sep. 30, 2025
Sep. 30, 2026
Sep. 30, 2025
Other Comprehensive Income (Loss)        
Other comprehensive income (loss), pre-tax $ (750.2) $ 510.8 $ (591.6) $ 1,124.0
Other comprehensive income (loss), tax 192.7 (108.5) 150.5 (212.6)
Other comprehensive income (loss) (557.5) 402.3 (441.1) 911.4
Net unrealized gains (losses) on available-for-sale securities including NCI        
Other Comprehensive Income (Loss)        
Other comprehensive income (loss) before reclassifications, pre-tax (3,037.7) 863.9 (3,649.4) 1,804.2
Adjustments for assumed changes in amortization patterns, pre-tax 2.1 (0.8) 2.5 (1.3)
Adjustments for assumed changes in policyholder liabilities, pre-tax 30.0 (1.7) 39.9 14.0
Other comprehensive income (loss), pre-tax (2,978.9) 882.4 (3,472.9) 1,944.9
Other comprehensive income (loss) before reclassifications, tax 650.7 (187.0) 787.1 (385.5)
Reclassification from accumulated other comprehensive income, tax (5.7) (4.3) (28.5) (26.9)
Adjustments for assumed changes in amortization patterns, tax (0.5) 0.1 (0.5) 0.3
Adjustments for assumed changes in policyholder liabilities, tax (6.3) 0.4 (8.4) (2.9)
Other comprehensive income (loss), tax 638.2 (190.8) 749.7 (415.0)
Other comprehensive income (loss) before reclassifications, after-tax (2,387.0) 676.9 (2,862.3) 1,418.7
Reclassification from accumulated other comprehensive income, after-tax 21.0 16.7 105.6 101.1
Adjustments for assumed changes in amortization patterns, after-tax 1.6 (0.7) 2.0 (1.0)
Adjustments for assumed changes in policyholder liabilities, after-tax 23.7 (1.3) 31.5 11.1
Other comprehensive income (loss) (2,340.7) 691.6 (2,723.2) 1,529.9
Net unrealized gains (losses) on available-for-sale securities including NCI | Location, Statement of Income, Balance [Axis]: us-gaap:GainLossOnInvestments        
Other Comprehensive Income (Loss)        
Reclassification from accumulated other comprehensive income, pre-tax 26.7 21.0 134.1 128.0
Net unrealized gains (losses) on derivative instruments including NCI        
Other Comprehensive Income (Loss)        
Other comprehensive income (loss) before reclassifications, pre-tax (104.6) 90.8 (63.4) (98.7)
Reclassification from accumulated other comprehensive income, pre-tax (0.1) (3.1) 0.1 (4.3)
Adjustments for assumed changes in amortization patterns, pre-tax     0.1 0.1
Other comprehensive income (loss), pre-tax (104.7) 87.7 (63.2) (102.9)
Other comprehensive income (loss) before reclassifications, tax 22.0 (19.0) 13.3 20.7
Reclassification from accumulated other comprehensive income, tax   0.6   0.9
Adjustments for assumed changes in amortization patterns, tax     (0.1)  
Other comprehensive income (loss), tax 22.0 (18.4) 13.2 21.6
Other comprehensive income (loss) before reclassifications, after-tax (82.6) 71.8 (50.1) (78.0)
Reclassification from accumulated other comprehensive income, after-tax (0.1) (2.5) 0.1 (3.4)
Adjustments for assumed changes in amortization patterns, after-tax       0.1
Other comprehensive income (loss) (82.7) 69.3 (50.0) (81.3)
Liability for future policy benefits discount rate remeasurement gain (loss)        
Other Comprehensive Income (Loss)        
Other comprehensive income (loss), pre-tax 2,193.2 (460.5) 2,788.3 (880.1)
Other comprehensive income (loss), tax (482.5) 97.2 (617.1) 184.5
Other comprehensive income (loss) 1,710.7 (363.3) 2,171.2 (695.6)
Market risk benefit nonperformance risk remeasurement gain(loss)        
Other Comprehensive Income (Loss)        
Other comprehensive income (loss), pre-tax 7.4 (5.9) 8.2 (3.7)
Other comprehensive income (loss), tax (1.5) 1.3 (1.7) 0.8
Other comprehensive income (loss) 5.9 (4.6) 6.5 (2.9)
Foreign currency translation adjustment including NCI        
Other Comprehensive Income (Loss)        
Other comprehensive income (loss) before reclassifications, pre-tax (65.7)   (56.9)  
Reclassification from accumulated other comprehensive income, pre-tax 196.3   197.8  
Other comprehensive income (loss), pre-tax 130.6 2.8 140.9 166.5
Other comprehensive income (loss) before reclassifications, tax 15.6   6.8  
Reclassification from accumulated other comprehensive income, tax 1.5   1.5  
Other comprehensive income (loss), tax 17.1 3.4 8.3 (4.6)
Other comprehensive income (loss) before reclassifications, after-tax (50.1)   (50.1)  
Reclassification from accumulated other comprehensive income, after-tax 197.8   199.3  
Other comprehensive income (loss) 147.7 6.2 149.2 161.9
Unrecognized postretirement benefit obligation including NCI        
Other Comprehensive Income (Loss)        
Other comprehensive income (loss) before reclassifications, pre-tax   0.1 (2.0) (13.5)
Other comprehensive income (loss), pre-tax 2.2 4.3 7.1 (0.7)
Other comprehensive income (loss) before reclassifications, tax   (0.1) 0.5 3.4
Reclassification from accumulated other comprehensive income, tax (0.6) (1.1) (2.4) (3.3)
Other comprehensive income (loss), tax (0.6) (1.2) (1.9) 0.1
Other comprehensive income (loss) before reclassifications, after-tax     (1.5) (10.1)
Reclassification from accumulated other comprehensive income, after-tax 1.6 3.1 6.7 9.5
Other comprehensive income (loss) 1.6 3.1 5.2 (0.6)
Unrecognized postretirement benefit obligation including NCI | Location, Statement of Income, Balance [Axis]: pfg:OperatingExpensesIncludingDeferredAcquisitionCostsCapitalizationAndAmortization        
Other Comprehensive Income (Loss)        
Reclassification from accumulated other comprehensive income, pre-tax $ 2.2 $ 4.2 $ 9.1 $ 12.8