INVESTMENT SECURITIES - Schedule of Investment Securities Maturity Information (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Investment securities available for sale
Non-amortizing securities maturing in one year or less, amortized cost	$ 6,014	$ 5,674
Non-amortizing securities maturing in after one through five years, amortized cost	5,880	4,996
Non-amortizing securities maturing in after five through 10 years, amortized cost	373	408
Non-amortizing securities maturing in after 10 years, amortized cost	22	17
Amortized Cost	28,502	20,688
Non-amortizing securities maturing in one year or less, fair value	6,013	5,658
Non-amortizing securities maturing in after one through five years, fair value	5,925	4,959
Non-amortizing securities maturing in after five through 10 years, fair value	352	369
Non-amortizing securities maturing in after 10 years, fair value	21	16
Investment securities available for sale, fair value	28,190	19,936
Investment securities held to maturity
Non-amortizing securities maturing in one year or less, amortized cost	186	27
Non-amortizing securities maturing in after one through five years, amortized cost	1,564	1,636
Non-amortizing securities maturing in after five through 10 years, amortized cost	545	622
Amortized Cost	10,391	9,979
Non-amortizing securities maturing in one year or less, fair value	182	26
Non-amortizing securities maturing in after one through five years, fair value	1,477	1,508
Non-amortizing securities maturing in after five through 10 years, fair value	485	533
Investment securities held to maturity, cost, fair value	9,168	8,503
Government agency
Investment securities available for sale
Without single maturity date, amortized cost	87	120
Without single maturity date, fair value	85	117
Residential mortgage-backed securities
Investment securities available for sale
Without single maturity date, amortized cost	13,201	7,154
Without single maturity date, fair value	13,016	6,686
Investment securities held to maturity
Without single maturity date, amortized cost	4,667	4,205
Without single maturity date, fair value	4,159	3,561
Commercial mortgage-backed securities
Investment securities available for sale
Without single maturity date, amortized cost	2,925	2,319
Without single maturity date, fair value	2,778	2,131
Investment securities held to maturity
Without single maturity date, amortized cost	3,429	3,489
Without single maturity date, fair value	$ 2,865	$ 2,875