Loans and ACL - Allowance for Credit Losses (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Provision for credit losses	$ 135	$ 126	$ 420	$ 409
Commercial \| Commercial and industrial
Financing Receivable, Allowance for Credit Losses [Roll Forward]
ACL, beginning balance	535	515	522	530
Charge-Offs	(28)	(13)	(74)	(72)
Recoveries	13	8	32	24
Provision for credit losses	21	7	61	35
ACL, ending balance	541	517	541	517
Commercial \| CRE
Financing Receivable, Allowance for Credit Losses [Roll Forward]
ACL, beginning balance	191	166	160	145
Charge-Offs	0	(4)	(8)	(8)
Recoveries	1	3	4	12
Provision for credit losses	(1)	0	35	16
ACL, ending balance	191	165	191	165
Commercial \| Lease financing
Financing Receivable, Allowance for Credit Losses [Roll Forward]
ACL, beginning balance	10	9	9	7
Charge-Offs	(1)	(2)	(3)	(4)
Recoveries	0	1	1	1
Provision for credit losses	1	2	3	6
ACL, ending balance	10	10	10	10
Retail \| Residential mortgage
Financing Receivable, Allowance for Credit Losses [Roll Forward]
ACL, beginning balance	221	211	209	227
Charge-Offs	(4)	(7)	(13)	(39)
Recoveries	0	0	1	1
Provision for credit losses	8	3	28	18
ACL, ending balance	225	207	225	207
Retail \| Direct
Financing Receivable, Allowance for Credit Losses [Roll Forward]
ACL, beginning balance	97	100	106	103
Charge-Offs	(17)	(16)	(53)	(46)
Recoveries	6	6	18	19
Provision for credit losses	11	11	26	25
ACL, ending balance	97	101	97	101
Retail \| Indirect
Financing Receivable, Allowance for Credit Losses [Roll Forward]
ACL, beginning balance	353	353	348	327
Charge-Offs	(94)	(103)	(283)	(298)
Recoveries	15	14	47	47
Provision for credit losses	79	86	241	274
ACL, ending balance	353	350	353	350
Revolving credit
Financing Receivable, Allowance for Credit Losses [Roll Forward]
ACL, beginning balance	105	101	108	106
Charge-Offs	(20)	(17)	(62)	(57)
Recoveries	4	4	14	14
Provision for credit losses	22	13	51	38
ACL, ending balance	111	101	111	101
PCI
Financing Receivable, Allowance for Credit Losses [Roll Forward]
ACL, beginning balance	18	30	28	44
Charge-Offs	(2)	(1)	(2)	(1)
Recoveries	0	0	0	0
Provision for credit losses	(6)	(2)	(16)	(16)
ACL, ending balance	10	27	10	27
ALLL
Financing Receivable, Allowance for Credit Losses [Roll Forward]
ACL, beginning balance	1,530	1,485	1,490	1,489
Charge-Offs	(166)	(163)	(498)	(525)
Recoveries	39	36	117	118
Provision for credit losses	135	120	429	396
ACL, ending balance	1,538	1,478	1,538	1,478
RUFC
Financing Receivable, Allowance for Credit Losses [Roll Forward]
ACL, beginning balance	110	117	119	110
Charge-Offs	0	0	0	0
Recoveries	0	0	0	0
Provision for credit losses	0	6	(9)	13
ACL, ending balance	110	123	110	123
ACL
Financing Receivable, Allowance for Credit Losses [Roll Forward]
ACL, beginning balance	1,640	1,602	1,609	1,599
Charge-Offs	(166)	(163)	(498)	(525)
Recoveries	39	36	117	118
Provision for credit losses	135	126	420	409
ACL, ending balance	$ 1,648	$ 1,601	$ 1,648	$ 1,601

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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A valuation allowance for financing receivables that are expected to be uncollectible.

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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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.11)
-URI http://asc.fasb.org/extlink&oid=114873765&loc=SL114874048-224260

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585

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