Loans and ACL - Allowance for Credit Losses (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Provision for credit losses		$ (813)	$ 2,335	$ 615
Commercial: | Commercial and industrial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance		2,204	570	557
Charge-Offs		(243)	(412)	(101)
Recoveries		107	96	26
Provision for credit losses		(642)	952	88
Allowance for Loan and Lease Losses, Adjustments, Other	[1]	0	998	0
ACL, ending balance		1,426	2,204	570
Commercial: | CRE
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance		573	150	142
Charge-Offs		(10)	(78)	(33)
Recoveries		6	5	5
Provision for credit losses		(219)	414	36
Allowance for Loan and Lease Losses, Adjustments, Other	[1]	0	82	0
ACL, ending balance		350	573	150
Commercial: | Commercial construction
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance		81	52	48
Charge-Offs		(2)	(30)	0
Recoveries		4	11	3
Provision for credit losses		(31)	32	1
Allowance for Loan and Lease Losses, Adjustments, Other	[1]	0	16	0
ACL, ending balance		52	81	52
Consumer: | Residential mortgage
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance		368	176	232
Charge-Offs		(23)	(56)	(21)
Recoveries		12	10	2
Provision for credit losses		(49)	(27)	(37)
Allowance for Loan and Lease Losses, Adjustments, Other	[1]	0	265	0
ACL, ending balance		308	368	176
Consumer: | Residential home equity and direct
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance		714	107	104
Charge-Offs		(214)	(231)	(93)
Recoveries		79	66	30
Provision for credit losses		36	318	66
Allowance for Loan and Lease Losses, Adjustments, Other	[1]	0	454	0
ACL, ending balance		615	714	107
Consumer: | Indirect auto
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance		1,198	304	298
Charge-Offs		(336)	(378)	(370)
Recoveries		92	87	52
Provision for credit losses		68	367	324
Allowance for Loan and Lease Losses, Adjustments, Other	[1]	0	818	0
ACL, ending balance		1,022	1,198	304
Consumer: | Indirect other
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance		208	60	58
Charge-Offs		(57)	(60)	(62)
Recoveries		24	23	17
Provision for credit losses		20	35	47
Allowance for Loan and Lease Losses, Adjustments, Other	[1]	0	150	0
ACL, ending balance		195	208	60
Consumer: | Student
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance		130	0
Charge-Offs		(24)	(23)
Recoveries		1	1
Provision for credit losses		4	23
Allowance for Loan and Lease Losses, Adjustments, Other	[1]	6	129
ACL, ending balance		117	130	0
Credit card
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance		359	122	110
Charge-Offs		(150)	(182)	(109)
Recoveries		37	32	20
Provision for credit losses		104	212	101
Allowance for Loan and Lease Losses, Adjustments, Other	[1]	0	175	0
ACL, ending balance		350	359	122
PCI
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance		0	8	9
Charge-Offs			0	0
Recoveries			0	0
Provision for credit losses			0	(1)
Allowance for Loan and Lease Losses, Adjustments, Other	[1]		(8)	0
ACL, ending balance			0	8
ALLL
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance		5,835	1,549	1,558
Charge-Offs		(1,059)	(1,450)	(789)
Recoveries		362	331	155
Provision for credit losses		(709)	2,326	625
Allowance for Loan and Lease Losses, Adjustments, Other	[1]	6	3,079	0
ACL, ending balance		4,435	5,835	1,549
RUFC
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance		364	340	93
Charge-Offs		0	0	0
Recoveries		0	0	0
Provision for credit losses		(104)	9	(10)
Allowance for Loan and Lease Losses, Adjustments, Other	[1]	0	15	257
ACL, ending balance		260	364	340
ACL
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance		6,199	1,889	1,651
Charge-Offs		(1,059)	(1,450)	(789)
Recoveries		362	331	155
Provision for credit losses		(813)	2,335	615
Allowance for Loan and Lease Losses, Adjustments, Other	[1]	6	3,094	257
ACL, ending balance		$ 4,695	$ 6,199	$ 1,889

[1] Includes the amounts assumed in the Merger, adoption of CECL, the ALLL for PCD acquisitions, and other activity.