Fair Values of Assets and Liabilities - Fair Value Option (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Fair Value Disclosures [Abstract]
Fair value carrying amount, total loans	$ 2,887	$ 2,011
Contractual principal outstanding, total loans	2,848	1,994
Carrying amount over (under) contractual principal outstanding, total loans	39	17
Fair value carrying amount, time deposits	7,655	2,818
Contractual principal outstanding, time deposits	7,657	2,822
Carrying amount over (under) contractual principal outstanding, time deposits	(2)	(4)
Long-term debt	45	0
Contractual principal outstanding, long-term debt	45	0
Carrying amount over (under) contractual principal outstanding, long-term debt	0	0
Fair value, nonaccrual loans	1	1
Contractual principal outstanding, nonaccrual loans	1	1
Fair value, loans 90 days or more past due	3	4
Contractual principal outstanding, loans 90 days or more past due	$ 3	$ 4