Components of Other Comprehensive Income (Loss) - Schedule of Reclassification from AOCI (Details) - USD ($) $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items]
Interest and fees on loans and leases	$ 482			$ 557			$ 1,485	$ 1,190
Income tax expense (benefit)	63			2			222	20
Other expense	60			52			182	124
Amounts reclassified from AOCI	(235)	$ (311)	$ (236)	(539)	$ (57)	$ (16)	(781)	(612)
Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amounts reclassified from AOCI	3			1			7	4
Reclassification out of Accumulated Other Comprehensive Income | Securities AFS
Accumulated Other Comprehensive Income (Loss) [Line Items]
Securities gains (losses), net	0			1			0	1
Income tax expense (benefit)	0			0			0	0
Amounts reclassified from AOCI	0			1			0	1
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)			(6)	(5)
Income tax expense (benefit)	1			0			2	1
Amounts reclassified from AOCI	(1)			(2)			(4)	(4)
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	(2)
Other expense	3			3			9	9
Amounts reclassified from AOCI	$ 4			$ 2			$ 11	$ 7