Accumulated Other Comprehensive Income - Schedule of Reclassifications Out of AOCI (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other income	$ 11	$ 4	$ 17	$ 4
Income taxes	62	58	121	139
INCOME (LOSS) FROM CONTINUING OPERATIONS	273	286	492	597
Interest income — Loans	1,524	1,576	3,062	3,052
Interest expense — Long-term debt	(332)	(349)	(660)	(624)
Investment banking and debt placement fees	126	120	296	265
Other expense	636	622	1,310	1,323
Reclassification out of Accumulated Other Comprehensive Income | Unrealized gains (losses) on available for sale securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income (loss) from continuing operations before income taxes	(10)	0	(13)	0
Income taxes	(2)	0	(3)	0
INCOME (LOSS) FROM CONTINUING OPERATIONS	(8)	0	(10)	0
Reclassification out of Accumulated Other Comprehensive Income | Realized gains on available for sale securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other income	0	0	0	0
Reclassification out of Accumulated Other Comprehensive Income | Realized losses on available for sale securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other income	(10)	0	(13)	0
Reclassification out of Accumulated Other Comprehensive Income | Unrealized gains (losses) on derivative financial instruments
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income (loss) from continuing operations before income taxes	(200)	(246)	(415)	(461)
Income taxes	(48)	(58)	(99)	(109)
INCOME (LOSS) FROM CONTINUING OPERATIONS	(152)	(188)	(316)	(352)
Reclassification out of Accumulated Other Comprehensive Income | Unrealized gains (losses) on derivative financial instruments | Interest rate
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest income — Loans	(199)	(245)	(415)	(460)
Interest expense — Long-term debt	(1)	(1)	(1)	(1)
Investment banking and debt placement fees	0	0	1	0
Reclassification out of Accumulated Other Comprehensive Income | Net pension and postretirement benefit costs
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income (loss) from continuing operations before income taxes	(2)	(2)	(3)	(4)
Income taxes	0	0	(2)	(1)
INCOME (LOSS) FROM CONTINUING OPERATIONS	(2)	(2)	(1)	(3)
Reclassification out of Accumulated Other Comprehensive Income | Amortization of losses
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other expense	(2)	(2)	(4)	(5)
Reclassification out of Accumulated Other Comprehensive Income | Settlement loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other expense	0	0	0	0
Reclassification out of Accumulated Other Comprehensive Income | Amortization of unrecognized prior service credit
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other expense	$ 0	$ 0	$ 1	$ 1