v3.26.1
Premiums Receivable - Premiums Receivable and Agents' Balances (Details) - USD ($)
$ in Millions
Jun. 30, 2026
Mar. 31, 2026
Dec. 31, 2025
Jun. 30, 2025
Mar. 31, 2025
Dec. 31, 2024
Financing Receivable, Credit Quality Indicator [Line Items]            
Premiums Receivable, Gross $ 7,169   $ 6,458      
ACL (160) $ (153) (142) $ (135) $ (126) $ (117)
Premiums receivable and agents' balances, net of ACL 7,009   6,316      
Premiums receivable, excluding receivables for losses within a deductible and retrospectively-rated policy premiums ("loss sensitive business")            
Financing Receivable, Credit Quality Indicator [Line Items]            
Premiums Receivable, Gross 6,674   5,948      
ACL (137) (131) (120) (113) (105) (97)
Receivables for Loss Sensitive Business            
Financing Receivable, Credit Quality Indicator [Line Items]            
Premiums Receivable, Gross 495   510      
ACL (23) $ (22) (22) $ (22) $ (21) $ (20)
Receivables for Loss Sensitive Business | Standard & Poor's, AA Rating            
Financing Receivable, Credit Quality Indicator [Line Items]            
Premiums Receivable, Gross 96   98      
Receivables for Loss Sensitive Business | Standard & Poor's, A Rating [Member]            
Financing Receivable, Credit Quality Indicator [Line Items]            
Premiums Receivable, Gross 73   76      
Receivables for Loss Sensitive Business | Standard & Poor's, BBB Rating            
Financing Receivable, Credit Quality Indicator [Line Items]            
Premiums Receivable, Gross 194   206      
Receivables for Loss Sensitive Business | Standard & Poor's, BB Rating            
Financing Receivable, Credit Quality Indicator [Line Items]            
Premiums Receivable, Gross 90   89      
Receivables for Loss Sensitive Business | Standard & Poor's, Below BB Rating            
Financing Receivable, Credit Quality Indicator [Line Items]            
Premiums Receivable, Gross $ 42   $ 41