Loans and ACL - Allowance for Credit Losses (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Provision for credit losses	$ 135	$ 135	$ 285	$ 283
Commercial \| Commercial and industrial
Financing Receivable, Allowance for Credit Losses [Roll Forward]
ACL, beginning balance	522	524	522	530
Charge-Offs	(23)	(26)	(46)	(59)
Recoveries	11	9	19	16
Provision for credit losses	25	8	40	28
ACL, ending balance	535	515	535	515
Commercial \| CRE
Financing Receivable, Allowance for Credit Losses [Roll Forward]
ACL, beginning balance	175	141	160	145
Charge-Offs	(2)	(3)	(8)	(4)
Recoveries	1	3	3	9
Provision for credit losses	17	25	36	16
ACL, ending balance	191	166	191	166
Commercial \| Lease financing
Financing Receivable, Allowance for Credit Losses [Roll Forward]
ACL, beginning balance	10	10	9	7
Charge-Offs	(1)	(1)	(2)	(2)
Recoveries	1	0	1	0
Provision for credit losses	0	0	2	4
ACL, ending balance	10	9	10	9
Retail \| Residential mortgage
Financing Receivable, Allowance for Credit Losses [Roll Forward]
ACL, beginning balance	216	223	209	227
Charge-Offs	(5)	(20)	(9)	(32)
Recoveries	1	1	1	1
Provision for credit losses	9	7	20	15
ACL, ending balance	221	211	221	211
Retail \| Direct
Financing Receivable, Allowance for Credit Losses [Roll Forward]
ACL, beginning balance	99	102	106	103
Charge-Offs	(17)	(16)	(36)	(30)
Recoveries	6	7	12	13
Provision for credit losses	9	7	15	14
ACL, ending balance	97	100	97	100
Retail \| Indirect
Financing Receivable, Allowance for Credit Losses [Roll Forward]
ACL, beginning balance	347	338	348	327
Charge-Offs	(82)	(88)	(189)	(195)
Recoveries	17	16	32	33
Provision for credit losses	71	87	162	188
ACL, ending balance	353	353	353	353
Revolving credit
Financing Receivable, Allowance for Credit Losses [Roll Forward]
ACL, beginning balance	104	103	108	106
Charge-Offs	(21)	(19)	(42)	(40)
Recoveries	5	5	10	10
Provision for credit losses	17	12	29	25
ACL, ending balance	105	101	105	101
PCI
Financing Receivable, Allowance for Credit Losses [Roll Forward]
ACL, beginning balance	25	46	28	44
Charge-Offs	0	0	0	0
Recoveries	0	0	0	0
Provision for credit losses	(7)	(16)	(10)	(14)
ACL, ending balance	18	30	18	30
ALLL
Financing Receivable, Allowance for Credit Losses [Roll Forward]
ACL, beginning balance	1,498	1,487	1,490	1,489
Charge-Offs	(151)	(173)	(332)	(362)
Recoveries	42	41	78	82
Provision for credit losses	141	130	294	276
ACL, ending balance	1,530	1,485	1,530	1,485
RUFC
Financing Receivable, Allowance for Credit Losses [Roll Forward]
ACL, beginning balance	116	112	119	110
Charge-Offs	0	0	0	0
Recoveries	0	0	0	0
Provision for credit losses	(6)	5	(9)	7
ACL, ending balance	110	117	110	117
ACL
Financing Receivable, Allowance for Credit Losses [Roll Forward]
ACL, beginning balance	1,614	1,599	1,609	1,599
Charge-Offs	(151)	(173)	(332)	(362)
Recoveries	42	41	78	82
Provision for credit losses	135	135	285	283
ACL, ending balance	$ 1,640	$ 1,602	$ 1,640	$ 1,602

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

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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