Investment Securities - Summary (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2026	Dec. 31, 2025
Debt Securities, Available-for-Sale [Line Items]
Accrued interest available-for-sale debt securities	$ 9	$ 3
Debt securities
Cost	2,595
Estimated Fair Value	2,581
Equity securities
Cost	54	54
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(9)	(8)
Estimated Fair Value	44	46
Total Cost	2,648	1,056
Total Gross Unrealized Gains	2	2
Total Gross Unrealized Losses	(24)	(16)
Total Estimated Fair Value	2,625	1,043
State and municipal obligations
Debt securities
Cost	53	54
Gross Unrealized Gains	1	1
Gross Unrealized Losses	(7)	(7)
Estimated Fair Value	47	48
U.S. Government agency obligations
Debt securities
Cost	3	3
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	3	3
U.S. Government treasury obligations
Debt securities
Cost	1,635	138
Gross Unrealized Gains	0	1
Gross Unrealized Losses	(7)	0
Estimated Fair Value	1,628	138
Mortgage-backed securities
Debt securities
Cost	9	10
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	9	9
Foreign government bonds and obligations
Debt securities
Cost	813	717
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	813	717
Other
Debt securities
Cost	81	81
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	$ 81	$ 81

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