Components of Other Comprehensive Income (Loss) - Schedule of Reclassification from AOCI (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items]
Interest and fees on loans and leases	$ 496		$ 306		$ 1,003	$ 633
Income tax expense (benefit)	88		13		159	18
Other expense	68		43		173	93
Amounts reclassified from AOCI	(311)	$ (236)	(57)	$ (16)	(546)	(73)
Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amounts reclassified from AOCI	4		0		8	3
Reclassification out of Accumulated Other Comprehensive Income | Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Interest and fees on loans and leases	(2)		(2)		(4)	(2)
Income tax expense (benefit)	0		0		1	0
Amounts reclassified from AOCI	(2)		(2)		(3)	(2)
Reclassification out of Accumulated Other Comprehensive Income | Pension and Post-retirement Plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income tax expense (benefit)	1		(1)		2	(1)
Other expense	5		3		9	6
Amounts reclassified from AOCI	$ 6		$ 2		$ 11	$ 5