Long-Term Debt - Schedule of Aggregate Carrying Value of Long-Term Debt (Details) - USD ($) $ in Millions	Mar. 31, 2026	Dec. 31, 2025
Schedule of Long Term and Short Term Debt Instruments [Line Items]
Total long-term debt	$ 2,027	$ 2,030
Senior Notes \| 5.170% Senior Notes due 2027
Schedule of Long Term and Short Term Debt Instruments [Line Items]
Stated interest rate	5.17%
Total long-term debt	$ 399	399
Senior Notes \| 3.125% Senior Notes due 2031
Schedule of Long Term and Short Term Debt Instruments [Line Items]
Stated interest rate	3.125%
Total long-term debt	$ 497	496
Senior Notes \| 5.670% Senior Notes due 2032
Schedule of Long Term and Short Term Debt Instruments [Line Items]
Stated interest rate	5.67%
Total long-term debt	$ 348	348
Senior Notes \| 4.000% Senior Notes due 2051
Schedule of Long Term and Short Term Debt Instruments [Line Items]
Stated interest rate	4.00%
Total long-term debt	$ 490	490
Surplus notes due 2027
Schedule of Long Term and Short Term Debt Instruments [Line Items]
Total long-term debt	250	250
FHLBI bank loans due 2034 & 2035
Schedule of Long Term and Short Term Debt Instruments [Line Items]
Total long-term debt	$ 43	$ 47