Loans and ACL - Allowance for Credit Losses (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Provision for credit losses	$ 117	$ 135	$ 444	$ 420
Commercial \| Commercial and industrial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance	574	535	546	522
Charge-Offs	(28)	(28)	(67)	(74)
Recoveries	5	13	19	32
Provision for credit losses	25	21	78	61
ACL, ending balance	576	541	576	541
Commercial \| CRE
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance	201	191	190	160
Charge-Offs	(2)	0	(28)	(8)
Recoveries	3	1	7	4
Provision for credit losses	(6)	(1)	27	35
ACL, ending balance	196	191	196	191
Commercial \| Lease financing
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance	10	10	11	9
Charge-Offs	(1)	(1)	(2)	(3)
Recoveries	1	0	1	1
Provision for credit losses	0	1	0	3
ACL, ending balance	10	10	10	10
Retail \| Residential mortgage
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance	224	221	232	209
Charge-Offs	(3)	(4)	(13)	(13)
Recoveries	0	0	1	1
Provision for credit losses	(22)	8	(21)	28
ACL, ending balance	199	225	199	225
Retail \| Direct
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance	99	97	97	106
Charge-Offs	(22)	(17)	(62)	(53)
Recoveries	6	6	19	18
Provision for credit losses	17	11	46	26
ACL, ending balance	100	97	100	97
Retail \| Indirect
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance	359	353	356	348
Charge-Offs	(106)	(94)	(306)	(283)
Recoveries	15	15	51	47
Provision for credit losses	94	79	261	241
ACL, ending balance	362	353	362	353
Revolving credit
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance	120	105	117	108
Charge-Offs	(27)	(20)	(78)	(62)
Recoveries	6	4	16	14
Provision for credit losses	23	22	67	51
ACL, ending balance	122	111	122	111
PCI
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance	8	18	9	28
Charge-Offs	0	(2)	0	(2)
Recoveries	0	0	0	0
Provision for credit losses	0	(6)	(1)	(16)
ACL, ending balance	8	10	8	10
ALLL
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance	1,595	1,530	1,558	1,490
Charge-Offs	(189)	(166)	(556)	(498)
Recoveries	36	39	114	117
Provision for credit losses	131	135	457	429
ACL, ending balance	1,573	1,538	1,573	1,538
RUFC
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance	94	110	93	119
Charge-Offs	0	0	0	0
Recoveries	0	0	0	0
Provision for credit losses	(14)	0	(13)	(9)
ACL, ending balance	80	110	80	110
ACL
Financing Receivable, Allowance for Credit Loss [Roll Forward]
ACL, beginning balance	1,689	1,640	1,651	1,609
Charge-Offs	(189)	(166)	(556)	(498)
Recoveries	36	39	114	117
Provision for credit losses	117	135	444	420
ACL, ending balance	$ 1,653	$ 1,648	$ 1,653	$ 1,648

Amount of recovery of loans and lease receivables which had previously been fully or partially written-off as bad debts.

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- Definition

Amount of loans and leases that have been written off from both loan receivables and allowance reserve for credit loss.

+ References

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- Definition

Amount of allowance for credit loss on financing receivable. Excludes allowance for financing receivable covered under loss sharing agreement.

+ References

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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- Definition

Amount of expense related loan transactions, lease transactions, credit loss from transactions other than loan and lease transactions, and other loss based on assessment of uncollectability from the counterparty to reduce the account to their net realizable value.

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