Accumulated Other Comprehensive Income - Schedule of Reclassifications Out of AOCI (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net securities gains (losses)	$ (6)	$ (935)	$ (6)	$ (948)
INCOME (LOSS) FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	602	(506)	1,656	107
Income taxes	112	(95)	337	26
Income (loss) from continuing operations	490	(411)	1,319	81
Interest income — Loans	1,466	1,516	4,310	4,578
Interest expense — Long-term debt	(181)	(292)	(572)	(952)
Investment banking and debt placement fees	184	171	537	467
Other expense	(170)	(158)	(525)	(542)
Reclassification out of Accumulated Other Comprehensive Income | Unrealized gains (losses) on securities available for sale
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
INCOME (LOSS) FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	0	(935)	0	(948)
Income taxes	0	(223)	0	(227)
Income (loss) from continuing operations	0	(712)	0	(721)
Reclassification out of Accumulated Other Comprehensive Income | Realized gains on available for sale securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net securities gains (losses)	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]
Net securities gains (losses)	0	(935)	0	(948)
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	(98)	(187)	(283)	(602)
Income taxes	(24)	(45)	(68)	(144)
Income (loss) from continuing operations	(74)	(142)	(215)	(458)
Interest income — Loans	(98)	(184)	(281)	(599)
Interest expense — Long-term debt	0	0	(2)	(1)
Investment banking and debt placement fees	0	(3)	0	(2)
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)	(3)	(4)	(7)
Income taxes	0	(1)	(2)	(3)
Income (loss) from continuing operations	(2)	(2)	(2)	(4)
Reclassification out of Accumulated Other Comprehensive Income | Amortization of losses
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other expense	(2)	(3)	(5)	(8)
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