SECURITIES - Schedule of Investments in Continuous Loss Positions (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Fair Value
Less than 12 Months	$ 6,542	$ 3,044
12 Months or Longer	19,486	20,505
Total	26,028	23,549
Gross Unrealized Losses
Less than 12 Months	(46)	(24)
12 Months or Longer	(2,307)	(1,999)
Total	(2,353)	(2,023)
Mortgage-backed securities
Fair Value
Less than 12 Months	5,710	2,939
12 Months or Longer	16,264	16,653
Total	21,974	19,592
Gross Unrealized Losses
Less than 12 Months	(39)	(24)
12 Months or Longer	(2,132)	(1,857)
Total	(2,171)	(1,881)
U.S. Treasury and other
Fair Value
Less than 12 Months	758	49
12 Months or Longer	3,211	3,245
Total	3,969	3,294
Gross Unrealized Losses
Less than 12 Months	(7)	0
12 Months or Longer	(175)	(139)
Total	(182)	(139)
State and political subdivisions
Fair Value
Less than 12 Months	0
12 Months or Longer	1
Total	1
Gross Unrealized Losses
Less than 12 Months	0
12 Months or Longer	0
Total	0
Federal agencies and U.S. government sponsored entities
Fair Value
Less than 12 Months	5,710	2,939
12 Months or Longer	16,007	16,398
Total	21,717	19,337
Gross Unrealized Losses
Less than 12 Months	(39)	(24)
12 Months or Longer	(2,111)	(1,833)
Total	(2,150)	(1,857)
Other/non-agency
Fair Value
Less than 12 Months	0	0
12 Months or Longer	257	255
Total	257	255
Gross Unrealized Losses
Less than 12 Months	0	0
12 Months or Longer	(21)	(24)
Total	(21)	(24)
Collateralized loan obligations
Fair Value
Less than 12 Months	74	56
12 Months or Longer	10	607
Total	84	663
Gross Unrealized Losses
Less than 12 Months	0	0
12 Months or Longer	0	(3)
Total	$ 0	$ (3)