Accumulated Other Comprehensive Income - Reclassifications Out of AOCI (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest income — Loans	$ 923	$ 888	$ 1,760	$ 1,777
Interest expense — Long-term debt	(61)	(54)	(110)	(114)
Investment banking and debt placement fees	149	217	312	379
Income taxes	132	189	222	336
Net pension and postretirement benefit costs	607	623	1,237	1,247
INCOME (LOSS) FROM CONTINUING OPERATIONS	530	724	977	1,342
Reclassification out of Accumulated Other Comprehensive Income | Unrealized gains (losses) on derivative financial instruments
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment banking and debt placement fees	5	(1)	7	1
Income (loss) from continuing operations before income taxes	23	83	87	172
Income taxes	5	20	21	41
INCOME (LOSS) FROM CONTINUING OPERATIONS	18	63	66	131
Reclassification out of Accumulated Other Comprehensive Income | Unrealized gains (losses) on derivative financial instruments | Interest income – loans
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest income — Loans	19	85	82	173
Reclassification out of Accumulated Other Comprehensive Income | Unrealized gains (losses) on derivative financial instruments | Interest expense — Long-term debt
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest expense — Long-term debt	(1)	(1)	(2)	(2)
Reclassification out of Accumulated Other Comprehensive Income | Amortization of losses
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net pension and postretirement benefit costs	(3)	(4)	(7)	(9)
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)	(4)	(6)	(9)
Income taxes	0	(1)	(1)	(2)
INCOME (LOSS) FROM CONTINUING OPERATIONS	(2)	(3)	(5)	(7)
Reclassification out of Accumulated Other Comprehensive Income | Settlement loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net pension and postretirement benefit costs	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]
Net pension and postretirement benefit costs	$ 1	$ 0	$ 1	$ 0