Accumulated Other Comprehensive Income - Reclassifications Out of AOCI (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest income — Loans	$ 1,134	$ 882	$ 2,894	$ 2,659
Interest expense — Long-term debt	(146)	(54)	(256)	(168)
Investment banking and debt placement fees	154	235	466	614
Income taxes	124	165	346	501
Net pension and postretirement benefit costs	655	640	1,892	1,887
INCOME (LOSS) FROM CONTINUING OPERATIONS	540	643	1,517	1,985
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	2	(1)	9	0
Income (loss) from continuing operations before income taxes	(65)	77	22	250
Income taxes	(15)	18	5	59
INCOME (LOSS) FROM CONTINUING OPERATIONS	(50)	59	17	191
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	(66)	79	16	253
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)	(3)	(3)
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	(4)	(5)	(11)	(14)
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	(7)	0	(7)
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
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	(4)	(12)	(10)	(21)
Income taxes	(1)	(3)	(2)	(5)
INCOME (LOSS) FROM CONTINUING OPERATIONS	$ (3)	$ (9)	$ (8)	$ (16)