Loans and ACL - Allowance for Credit Losses (Details) - USD ($) $ in Millions		3 Months Ended
	Jan. 01, 2020	Mar. 31, 2020	Mar. 31, 2019
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Provision for credit losses		$ 893	$ 155
CECL impact on Allowance for Credit Losses
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Other (2)	$ 3,100
Commercial:
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Other (2)		411
Commercial: | Commercial and industrial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance	560	560	546
Charge-Offs		(39)	(17)
Recoveries		17	6
Provision for credit losses		371	13
ACL, ending balance		1,813	548
Commercial: | Commercial and industrial | CECL impact on Allowance for Credit Losses
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Other (2)		904
Commercial: | CRE
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance	150	150	142
Charge-Offs		(1)	(8)
Recoveries		0	0
Provision for credit losses		68	18
ACL, ending balance		299	152
Commercial: | CRE | CECL impact on Allowance for Credit Losses
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Other (2)		82
Commercial: | Commercial construction
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance	52	52	48
Charge-Offs		(3)	0
Recoveries		1	1
Provision for credit losses		22	(5)
ACL, ending balance		88	44
Commercial: | Commercial construction | CECL impact on Allowance for Credit Losses
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Other (2)		16
Commercial: | Lease financing
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance	10	10	11
Charge-Offs		(2)	(1)
Recoveries		0	0
Provision for credit losses		(23)	1
ACL, ending balance		79	11
Commercial: | Lease financing | CECL impact on Allowance for Credit Losses
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Other (2)		94
Consumer:
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Other (2)		130
Consumer: | Residential Mortgage
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance	176	176	232
Charge-Offs		(11)	(5)
Recoveries		2	1
Provision for credit losses		(4)	(3)
ACL, ending balance		427	225
Consumer: | Residential Mortgage | CECL impact on Allowance for Credit Losses
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Other (2)		264
Consumer: | Residential home equity and direct
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance	107	107	104
Charge-Offs		(68)	(20)
Recoveries		15	6
Provision for credit losses		102	13
ACL, ending balance		607	103
Consumer: | Residential home equity and direct | CECL impact on Allowance for Credit Losses
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Other (2)		451
Consumer: | Indirect auto
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance	304	304	298
Charge-Offs		(142)	(92)
Recoveries		23	13
Provision for credit losses		189	81
ACL, ending balance		1,192	300
Consumer: | Indirect auto | CECL impact on Allowance for Credit Losses
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Other (2)		818
Consumer: | Indirect other
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance	60	60	58
Charge-Offs		(18)	(17)
Recoveries		7	4
Provision for credit losses		12	13
ACL, ending balance		213	58
Consumer: | Indirect other | CECL impact on Allowance for Credit Losses
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Other (2)		152
Consumer: | Student
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance	0	0
Charge-Offs		(8)
Recoveries		0
Provision for credit losses		34
ACL, ending balance		146
Consumer: | Student | CECL impact on Allowance for Credit Losses
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Other (2)		120
Credit card
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance	122	122	110
Charge-Offs		(53)	(24)
Recoveries		8	6
Provision for credit losses		95	20
Other (2)		50
ACL, ending balance		347	112
Credit card | CECL impact on Allowance for Credit Losses
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Other (2)		175
PCI
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance	8	8	9
Charge-Offs		0	0
Recoveries		0	0
Provision for credit losses		0	(1)
ACL, ending balance		0	8
PCI | CECL impact on Allowance for Credit Losses
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Other (2)		(8)
ALLL
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance	1,549	1,549	1,558
Charge-Offs		(345)	(184)
Recoveries		73	37
Provision for credit losses		866	150
ACL, ending balance		5,211	1,561
ALLL | CECL impact on Allowance for Credit Losses
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Other (2)		3,068
RUFC
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance	340	340	93
Charge-Offs		0	0
Recoveries		0	0
Provision for credit losses		27	5
Other (2)		(9)
ACL, ending balance		400	98
RUFC | CECL impact on Allowance for Credit Losses
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Other (2)		33
ACL
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance	$ 1,889	1,889	1,651
Charge-Offs		(345)	(184)
Recoveries		73	37
Provision for credit losses		893	155
ACL, ending balance		5,611	$ 1,659
ACL | CECL impact on Allowance for Credit Losses
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Other (2)		$ 3,101