Loans and ACL - Allowance for Credit Losses (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Provision for credit losses	$ 844	$ 172	$ 1,737	$ 327
Commercial: | Commercial and industrial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance	1,813	548	560	546
Charge-Offs	(123)	(22)	(162)	(39)
Allowance for Loan and Lease Losses, Adjustments, Other	0	0	904	0
Recoveries	21	8	38	14
Provision for credit losses	426	40	797	53
ACL, ending balance	2,137	574	2,137	574
Commercial: | CRE
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance	299	152	150	142
Charge-Offs	(14)	(18)	(15)	(26)
Allowance for Loan and Lease Losses, Adjustments, Other	0	0	82	0
Recoveries	4	2	4	2
Provision for credit losses	102	21	170	39
ACL, ending balance	391	157	391	157
Commercial: | Commercial construction
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance	88	44	52	48
Charge-Offs	0	0	(3)	0
Allowance for Loan and Lease Losses, Adjustments, Other	0	0	16	0
Recoveries	7	1	8	2
Provision for credit losses	39	(1)	61	(6)
ACL, ending balance	134	44	134	44
Commercial: | Lease financing
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance	79	11	10	11
Charge-Offs	(4)	0	(6)	(1)
Allowance for Loan and Lease Losses, Adjustments, Other	0	0	94	0
Recoveries	0	0	0	0
Provision for credit losses	(16)	(1)	(39)	0
ACL, ending balance	59	10	59	10
Consumer: | Residential Mortgage
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance	427	225	176	232
Charge-Offs	(35)	(5)	(46)	(10)
Allowance for Loan and Lease Losses, Adjustments, Other	1	0	265	0
Recoveries	2	0	4	1
Provision for credit losses	36	4	32	1
ACL, ending balance	431	224	431	224
Consumer: | Residential home equity and direct
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance	607	103	107	104
Charge-Offs	(65)	(24)	(133)	(44)
Allowance for Loan and Lease Losses, Adjustments, Other	3	0	454	0
Recoveries	15	8	30	14
Provision for credit losses	137	19	239	32
ACL, ending balance	697	106	697	106
Consumer: | Indirect auto
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance	1,192	300	304	298
Charge-Offs	(80)	(79)	(222)	(171)
Allowance for Loan and Lease Losses, Adjustments, Other	0	0	818	0
Recoveries	18	14	41	27
Provision for credit losses	60	65	249	146
ACL, ending balance	1,190	300	1,190	300
Consumer: | Indirect other
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance	213	58	60	58
Charge-Offs	(20)	(12)	(38)	(29)
Allowance for Loan and Lease Losses, Adjustments, Other	(2)	0	150	0
Recoveries	7	5	14	9
Provision for credit losses	15	8	27	21
ACL, ending balance	213	59	213	59
Consumer: | Student
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance	146		0
Charge-Offs	(6)		(14)
Allowance for Loan and Lease Losses, Adjustments, Other	3		123
Recoveries	1		1
Provision for credit losses	(21)		13
ACL, ending balance	123		123
Credit card
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance	347	112	122	110
Charge-Offs	(50)	(23)	(103)	(47)
Allowance for Loan and Lease Losses, Adjustments, Other	0	0	175	0
Recoveries	6	3	14	9
Provision for credit losses	24	21	119	41
ACL, ending balance	327	113	327	113
PCI
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance		8	8	9
Charge-Offs		0	0	0
Allowance for Loan and Lease Losses, Adjustments, Other		0	(8)	0
Recoveries		0	0	0
Provision for credit losses		0	0	(1)
ACL, ending balance	0	8	0	8
ALLL
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance	5,211	1,561	1,549	1,558
Charge-Offs	(397)	(183)	(742)	(367)
Allowance for Loan and Lease Losses, Adjustments, Other	5	0	3,073	0
Recoveries	81	41	154	78
Provision for credit losses	802	176	1,668	326
ACL, ending balance	5,702	1,595	5,702	1,595
RUFC
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance	400	98	340	93
Charge-Offs	0	0	0	0
Allowance for Loan and Lease Losses, Adjustments, Other	(11)	0	22	0
Recoveries	0	0	0	0
Provision for credit losses	42	(4)	69	1
ACL, ending balance	431	94	431	94
ACL
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance	5,611	1,659	1,889	1,651
Charge-Offs	(397)	(183)	(742)	(367)
Allowance for Loan and Lease Losses, Adjustments, Other	(6)	0	3,095	0
Recoveries	81	41	154	78
Provision for credit losses	844	172	1,737	327
ACL, ending balance	$ 6,133	$ 1,689	$ 6,133	$ 1,689