LONG-TERM DEBT AND SHAREHOLDERS' EQUITY (Amounts Reclassified from AOCI) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Accumulated Other Comprehensive Income (Loss) [Line Items]
Interest and fees on loans; Interest on short- and long-term borrowings	$ 899	$ 831	$ 2,641	$ 2,348
Less: Income tax expense (benefit)	63	53	174	182
Net income	214	175	568	554
Net unrealized gains/(losses) on investment securities | Amounts reclassified from AOCI
Accumulated Other Comprehensive Income (Loss) [Line Items]
Securities gains (losses), net	(67)	(74)	(195)	(210)
Less: Income tax expense (benefit)	(16)	(18)	(48)	(51)
Net income	(51)	(56)	(147)	(159)
Net unrealized gains/(losses) on derivatives and other | Amounts reclassified from AOCI
Accumulated Other Comprehensive Income (Loss) [Line Items]
Interest and fees on loans; Interest on short- and long-term borrowings	(28)	(39)	(93)	(128)
Less: Income tax expense (benefit)	(7)	(10)	(23)	(32)
Net income	$ (21)	$ (29)	$ (70)	$ (96)