INVESTMENT SECURITIES - Schedule of Investment Securities Maturity Information (Details) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Investment securities available for sale
Non-amortizing securities maturing in one year or less, amortized cost	$ 5,503	$ 5,090
Non-amortizing securities maturing in after one through five years, amortized cost	7,727	8,945
Non-amortizing securities maturing in after five through 10 years, amortized cost	353	346
Non-amortizing securities maturing in after 10 years, amortized cost	22	22
Amortized Cost	34,340	34,512
Non-amortizing securities maturing in one year or less, fair value	5,508	5,086
Non-amortizing securities maturing in after one through five years, fair value	7,764	8,949
Non-amortizing securities maturing in after five through 10 years, fair value	338	330
Non-amortizing securities maturing in after 10 years, fair value	22	22
Investment securities available for sale, fair value	33,900	33,750
Investment securities held to maturity
Non-amortizing securities maturing in one year or less, amortized cost	450	429
Non-amortizing securities maturing in after one through five years, amortized cost	1,281	1,299
Non-amortizing securities maturing in after five through 10 years, amortized cost	547	546
Amortized Cost	10,324	10,239
Non-amortizing securities maturing in one year or less, fair value	443	419
Non-amortizing securities maturing in after one through five years, fair value	1,209	1,208
Non-amortizing securities maturing in after five through 10 years, fair value	483	468
Investment securities held to maturity, cost, fair value	8,973	8,702
Government agency
Investment securities available for sale
Without single maturity date, amortized cost	71	79
Without single maturity date, fair value	69	77
Residential mortgage-backed securities
Investment securities available for sale
Without single maturity date, amortized cost	16,905	16,161
Without single maturity date, fair value	16,605	15,620
Investment securities held to maturity
Without single maturity date, amortized cost	4,668	4,558
Without single maturity date, fair value	4,090	3,878
Commercial mortgage-backed securities
Investment securities available for sale
Without single maturity date, amortized cost	3,759	3,869
Without single maturity date, fair value	3,594	3,666
Investment securities held to maturity
Without single maturity date, amortized cost	3,378	3,407
Without single maturity date, fair value	$ 2,748	$ 2,729