v3.26.1
Fair Value Measurements - Narrative (Details)
$ / shares in Units, $ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2026
USD ($)
pricingMethod
$ / shares
Jun. 30, 2025
USD ($)
Jun. 30, 2026
USD ($)
pricingMethod
$ / shares
Jun. 30, 2025
USD ($)
Dec. 31, 2025
USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]          
Number of pricing methods | pricingMethod 3   3    
Fair value option, debt securities $ 3,534   $ 3,534   $ 3,470
Debt securities 55,742   55,742   50,791
Transfers from Level 3 to Level 2 70 $ 46 105 $ 104  
Transfers from Level 2 to Level 3 65 (9) 7 165  
Transfers from Level NAV to Level 3 $ 20 $ 0 $ 29 $ 0  
FHLBI capital stock, stock price (in usd per share) | $ / shares $ 100   $ 100    
Unobservable Inputs | Level 3          
Fair Value Measurement Inputs and Valuation Techniques [Line Items]          
Debt securities $ 63   $ 63   117
Funds withheld assets          
Fair Value Measurement Inputs and Valuation Techniques [Line Items]          
Fair value option, assets carrying amount 4,393   4,393   3,867
Fair Value          
Fair Value Measurement Inputs and Valuation Techniques [Line Items]          
Fair value option, market risk benefit, debt securities 705   705   766
Debt securities 55,742   55,742   50,791
Variable Interest Entity, Primary Beneficiary          
Fair Value Measurement Inputs and Valuation Techniques [Line Items]          
Fair value option, debt securities 2,648   2,648   2,698
Other Liabilities 184   184   258
Variable Interest Entity, Primary Beneficiary | Fair Value          
Fair Value Measurement Inputs and Valuation Techniques [Line Items]          
Other Liabilities $ 2,474   $ 2,474   $ 2,578