Accumulated Other Comprehensive Income - Reclassifications Out of AOCI (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other income	[1]	$ 13	$ 33	$ 64	$ (55)
Income (loss) from continuing operations before income taxes		919	222	1,691	398
Income taxes		189	30	336	53
Interest income — Loans		888	980	1,777	2,006
Interest expense — Long-term debt		(54)	(71)	(114)	(161)
Investment banking and debt placement fees		217	156	379	272
Other expense		623	572	1,247	1,087
INCOME (LOSS) FROM CONTINUING OPERATIONS		724	185	1,342	330
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		83	89	172	122
Income taxes		20	21	41	29
Investment banking and debt placement fees		(1)	0	1	0
INCOME (LOSS) FROM CONTINUING OPERATIONS		63	68	131	93
Reclassification out of Accumulated Other Comprehensive Income | Amortization of losses
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other expense		(4)	(4)	(9)	(8)
Reclassification out of Accumulated Other Comprehensive Income | Settlement loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other expense		0	(4)	0	(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		(4)	(8)	(9)	(16)
Income taxes		(1)	(2)	(2)	(4)
INCOME (LOSS) FROM CONTINUING OPERATIONS		(3)	(6)	(7)	(12)
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		85	90	173	124
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)	$ (2)	$ (2)

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