Accumulated Other Comprehensive Income - Reclassifications Out of AOCI (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest income — Loans	$ 837	$ 889
Interest expense — Long-term debt	(49)	(60)
Investment banking and debt placement fees	163	162
Income taxes	90	147
Other expense	630	624
INCOME (LOSS) FROM CONTINUING OPERATIONS	447	618
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
Income (loss) from continuing operations before income taxes	65	89
Income taxes	15	21
INCOME (LOSS) FROM CONTINUING OPERATIONS	50	68
Reclassification out of Accumulated Other Comprehensive Income | Amortization of losses
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other expense	(4)	(5)
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)	(5)
Income taxes	(1)	(1)
INCOME (LOSS) FROM CONTINUING OPERATIONS	(3)	(4)
Interest income – loans | Reclassification out of Accumulated Other Comprehensive Income | Unrealized gains (losses) on derivative financial instruments
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest income — Loans	64	89
Interest expense — Long-term debt | Reclassification out of Accumulated Other Comprehensive Income | Unrealized gains (losses) on derivative financial instruments
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest expense — Long-term debt	$ (1)	$ (1)