Accumulated Other Comprehensive Income - Reclassification Out of AOCI (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Securities gains (losses), net	$ 3	$ (24)
Interest and fees on loans and leases	1,030	1,235
Compensation and benefits	706	647
Income (loss) before income taxes	883	60
Applicable income tax expense	(189)	(14)
Net income	694	46
Reclassification out of AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Net income	45	24
Reclassification out of AOCI | Net unrealized gains on available-for-sale debt securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Securities gains (losses), net	(15)	0
Income (loss) before income taxes	(15)	0
Applicable income tax expense	4	0
Net income	(11)	0
Reclassification out of AOCI | Net unrealized gains on cash flow hedge
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Interest and fees on loans and leases	72	32
Income (loss) before income taxes	72	32
Applicable income tax expense	(15)	(7)
Net income	57	25
Reclassification out of AOCI | Net periodic benefit costs
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Compensation and benefits	(2)	(1)
Income (loss) before income taxes	(2)	(1)
Applicable income tax expense	1	0
Net income	$ (1)	$ (1)