Accumulated Other Comprehensive Income - Reclassifications Out of AOCI (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other income	[1]	$ 33	$ 17	$ (55)	$ 27
Interest income — Loans		980	1,082	2,006	2,148
Interest expense — Long-term debt		(71)	(120)	(161)	(240)
Income (loss) from continuing operations before income taxes		222	518	398	1,014
Income taxes		30	87	53	169
Other expense		572	589	1,087	1,152
INCOME (LOSS) FROM CONTINUING OPERATIONS		185	423	330	829
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]
Other income				4	0
Income (loss) from continuing operations before income taxes				4	0
Income taxes				1	0
INCOME (LOSS) FROM CONTINUING OPERATIONS				3	0
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		89	(19)	122	(44)
Income taxes		21	(4)	29	(10)
INCOME (LOSS) FROM CONTINUING OPERATIONS		68	(15)	93	(34)
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		(8)	(3)	(16)	(7)
Income taxes		(2)	(1)	(4)	(2)
INCOME (LOSS) FROM CONTINUING OPERATIONS		(6)	(2)	(12)	(5)
Reclassification out of Accumulated Other Comprehensive Income | Net pension and postretirement benefit costs | Amortization of losses
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other expense		(4)	(3)	(8)	(7)
Reclassification out of Accumulated Other Comprehensive Income | Net pension and postretirement benefit costs | Settlement loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other expense		(4)	0	(8)	0
Interest income – loans | Reclassification out of Accumulated Other Comprehensive Income | Unrealized gains (losses) on derivative financial instruments | Interest rate
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest income — Loans		90	(19)	124	(43)
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)	$ 0	$ (2)	$ (1)

[1] 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. For the three and six months ended June 30, 2019, net securities gains (losses) totaled less than $1 million. For the three months ended June 30, 2020, and June 30, 2019, we did not have any impairment losses related to securities.