INVESTMENT SECURITIES - Schedule of Gross Unrealized Losses and Fair Value by Investment Category (Details) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Fair Value
Less than 12 months	$ 5,593	$ 7,198
12 months or more	8,788	9,104
Total	14,381	16,302
Gross Unrealized Losses
Less than 12 months	(82)	(178)
12 months or more	(1,081)	(1,231)
Total	(1,163)	(1,409)
U.S. Treasury and agency obligations
Fair Value
Less than 12 months	1,790	2,343
12 months or more	432	456
Total	2,222	2,799
Gross Unrealized Losses
Less than 12 months	(28)	(68)
12 months or more	(33)	(42)
Total	(61)	(110)
Mortgage-backed securities
Fair Value
Less than 12 months	1,471	1,766
12 months or more	2,200	2,203
Total	3,671	3,969
Gross Unrealized Losses
Less than 12 months	(23)	(50)
12 months or more	(405)	(459)
Total	(428)	(509)
Tax-exempt municipal securities
Fair Value
Less than 12 months	71	97
12 months or more	393	405
Total	464	502
Gross Unrealized Losses
Less than 12 months	(1)	(1)
12 months or more	(23)	(21)
Total	(24)	(22)
Residential
Fair Value
Less than 12 months	42	130
12 months or more	341	343
Total	383	473
Gross Unrealized Losses
Less than 12 months	(1)	(2)
12 months or more	(54)	(62)
Total	(55)	(64)
Commercial
Fair Value
Less than 12 months	108	58
12 months or more	930	992
Total	1,038	1,050
Gross Unrealized Losses
Less than 12 months	(1)	(1)
12 months or more	(71)	(84)
Total	(72)	(85)
Asset-backed securities
Fair Value
Less than 12 months	327	419
12 months or more	388	436
Total	715	855
Gross Unrealized Losses
Less than 12 months	(3)	(5)
12 months or more	(15)	(19)
Total	(18)	(24)
Corporate debt securities
Fair Value
Less than 12 months	1,784	2,385
12 months or more	4,104	4,269
Total	5,888	6,654
Gross Unrealized Losses
Less than 12 months	(25)	(51)
12 months or more	(480)	(544)
Total	$ (505)	$ (595)