Accumulated Other Comprehensive Income - Reclassification 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 on Derivatives [Line Items]
Securities gains (losses), net	$ (1)	$ 51	$ 12	$ 48
Interest and fees on loans and leases	1,014	1,047	3,078	3,397
Compensation and benefits	627	637	1,971	1,911
Income before income taxes	895	746	2,689	1,051
Applicable income tax expense	(191)	(165)	(582)	(228)
Net income	704	581	2,107	823
Reclassification out of AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Net income	57	87	161	159
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	1	45	(9)	45
Income before income taxes	1	45	(9)	45
Applicable income tax expense	0	(11)	2	(11)
Net income	1	34	(7)	34
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	74	72	219	165
Income before income taxes	74	72	219	165
Applicable income tax expense	(16)	(16)	(46)	(35)
Net income	58	56	173	130
Reclassification out of AOCI | Net periodic benefit costs
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Compensation and benefits	(2)	(2)	(5)	(5)
Income before income taxes	(3)	(4)	(7)	(7)
Applicable income tax expense	1	1	2	2
Net income	(2)	(3)	(5)	(5)
Reclassification out of AOCI | Settlements
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Compensation and benefits	$ (1)	$ (2)	$ (2)	$ (2)