SECURITIES - Schedule of Investments (Details) - USD ($) $ in Millions		Jun. 30, 2024	Dec. 31, 2023
Debt Securities, Available-for-Sale, Fair Value to Amortized Cost, after Allowance for Credit Loss [Abstract]
Fair Value	[1]	$ 31,938	$ 29,777
Debt Securities, Held-to-Maturity, Fair Value to Amortized Cost, after Allowance for Credit Loss [Abstract]
Amortized Cost	[1]	8,895	9,184
Gross Unrealized Gains		1	9
Gross Unrealized Gains		(972)	(843)
Fair Value		7,924	8,350
Total equity securities, at cost, Amortized Cost		731	869
Equity securities, at cost, fair value		731	869
Equity Securities, Amortized Cost		192	173
Equity Securities, Fair Value		192	173
Portfolio level basis adjustments excluded from amortized cost		(113)	60
Total debt securities available for sale, at fair value
Debt Securities, Available-for-Sale, Fair Value to Amortized Cost, after Allowance for Credit Loss [Abstract]
Amortized Cost		34,334	31,729
Gross Unrealized Gains		36	71
Gross Unrealized Losses		(2,432)	(2,023)
Fair Value		31,938	29,777
U.S. Treasury and other
Debt Securities, Available-for-Sale, Fair Value to Amortized Cost, after Allowance for Credit Loss [Abstract]
Amortized Cost		5,198	4,493
Gross Unrealized Gains		5	26
Gross Unrealized Losses		(191)	(139)
Fair Value		5,012	4,380
State and political subdivisions
Debt Securities, Available-for-Sale, Fair Value to Amortized Cost, after Allowance for Credit Loss [Abstract]
Amortized Cost		1	1
Gross Unrealized Gains		0	0
Gross Unrealized Losses		0	0
Fair Value		1	1
Total mortgage-backed securities
Debt Securities, Available-for-Sale, Fair Value to Amortized Cost, after Allowance for Credit Loss [Abstract]
Amortized Cost		28,842	26,568
Gross Unrealized Gains		30	45
Gross Unrealized Losses		(2,241)	(1,881)
Fair Value		26,631	24,732
Debt Securities, Held-to-Maturity, Fair Value to Amortized Cost, after Allowance for Credit Loss [Abstract]
Amortized Cost		8,447	8,696
Gross Unrealized Gains		0	9
Gross Unrealized Gains		(957)	(818)
Fair Value		7,490	7,887
Federal agencies and U.S. government sponsored entities
Debt Securities, Available-for-Sale, Fair Value to Amortized Cost, after Allowance for Credit Loss [Abstract]
Amortized Cost		28,568	26,289
Gross Unrealized Gains		30	45
Gross Unrealized Losses		(2,220)	(1,857)
Fair Value		26,378	24,477
Debt Securities, Held-to-Maturity, Fair Value to Amortized Cost, after Allowance for Credit Loss [Abstract]
Amortized Cost		8,447	8,696
Gross Unrealized Gains		0	9
Gross Unrealized Gains		(957)	(818)
Fair Value		7,490	7,887
Other/non-agency
Debt Securities, Available-for-Sale, Fair Value to Amortized Cost, after Allowance for Credit Loss [Abstract]
Amortized Cost		274	279
Gross Unrealized Gains		0	0
Gross Unrealized Losses		(21)	(24)
Fair Value		253	255
Collateralized loan obligations
Debt Securities, Available-for-Sale, Fair Value to Amortized Cost, after Allowance for Credit Loss [Abstract]
Amortized Cost		293	667
Gross Unrealized Gains		1	0
Gross Unrealized Losses		0	(3)
Fair Value		294	664
Asset-backed securities
Debt Securities, Held-to-Maturity, Fair Value to Amortized Cost, after Allowance for Credit Loss [Abstract]
Amortized Cost		448	488
Gross Unrealized Gains		1	0
Gross Unrealized Gains		(15)	(25)
Fair Value		$ 434	$ 463

[1] Includes only collateral pledged by the Company where counterparties have the right to sell or pledge the collateral.