INVESTMENT SECURITIES - Schedule of Investment Securities Maturity Information (Details) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Investment securities available for sale
Non-amortizing securities maturing in one year or less, cost	$ 5,995	$ 5,674
Non-amortizing securities maturing in after one through five years, cost	5,962	4,996
Non-amortizing securities maturing in after five through 10 years, cost	382	408
Non-amortizing securities maturing in after 10 years, cost	22	17
Amortized Cost	27,959	20,688
Non-amortizing securities maturing in one year or less, fair value	5,961	5,658
Non-amortizing securities maturing in after one through five years, fair value	5,921	4,959
Non-amortizing securities maturing in after five through 10 years, fair value	351	369
Non-amortizing securities maturing in after 10 years, fair value	21	16
Investment securities available for sale, fair value	27,053	19,936
Investment securities held to maturity
Non-amortizing securities maturing in one year or less, cost	27	27
Non-amortizing securities maturing in after one through five years, cost	1,641	1,636
Non-amortizing securities maturing in after five through 10 years, cost	624	622
Amortized Cost	10,535	9,979
Non-amortizing securities maturing in one year or less, fair value	26	26
Non-amortizing securities maturing in after one through five years, fair value	1,514	1,508
Non-amortizing securities maturing in after five through 10 years, fair value	531	533
Investment securities held to maturity, cost, fair value	8,946	8,503
Government agency
Investment securities available for sale
Without single maturity date, cost	99	120
Without single maturity date, fair value	97	117
Residential mortgage-backed securities
Investment securities available for sale
Without single maturity date, cost	12,561	7,154
Without single maturity date, fair value	11,975	6,686
Investment securities held to maturity
Without single maturity date, cost	4,793	4,205
Without single maturity date, fair value	4,093	3,561
Commercial mortgage-backed securities
Investment securities available for sale
Without single maturity date, cost	2,938	2,319
Without single maturity date, fair value	2,727	2,131
Investment securities held to maturity
Without single maturity date, cost	3,450	3,489
Without single maturity date, fair value	$ 2,782	$ 2,875