Accumulated Other Comprehensive Income - Reclassifications Out of AOCI (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest income — Loans		$ 882	$ 927	$ 2,659	$ 2,933
Other income	[1]	25	28	89	(27)
Income taxes		165	60	501	113
Interest expense — Long-term debt		(54)	(64)	(168)	(225)
Investment banking and debt placement fees		235	146	614	418
Other expense		640	588	1,887	1,675
INCOME (LOSS) FROM CONTINUING OPERATIONS		643	424	1,985	754
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	4
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	4
Income taxes				0	1
INCOME (LOSS) FROM CONTINUING OPERATIONS				0	3
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		77	99	250	221
Income taxes		18	24	59	53
Investment banking and debt placement fees		(1)	0	0	0
INCOME (LOSS) FROM CONTINUING OPERATIONS		59	75	191	168
Reclassification out of Accumulated Other Comprehensive Income | Amortization of losses
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other expense		(5)	(5)	(14)	(13)
Reclassification out of Accumulated Other Comprehensive Income | Settlement loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other expense		(7)	0	(7)	(8)
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		(12)	(5)	(21)	(21)
Income taxes		(3)	(1)	(5)	(5)
INCOME (LOSS) FROM CONTINUING OPERATIONS		(9)	(4)	(16)	(16)
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		79	100	253	224
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)	$ (3)	$ (3)

[1] For the three and nine months ended September 30, 2021, net securities gains (losses) totaled less than $1 million. For the three months ended September 30, 2021 and September 30, 2020, we did not have any impairment losses related to securities. For the three months ended September 30, 2020, we had no net securities gains (losses). For the nine months ended September 30, 2020, net securities gains (losses) totaled $4 million.