Loans and ACL - Allowance for Credit Losses (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Provision for credit losses	$ 566	$ 547	$ 572
Commercial \| Commercial and industrial
Financing Receivable, Allowance for Credit Losses [Roll Forward]
ACL, beginning balance	522	530	488
Charge-Offs	(92)	(95)	(143)
Allowance for Loan and Lease Losses, Adjustments, Other	0	0	0
Recoveries	39	36	44
Provision for credit losses	77	51	141
ACL, ending balance	546	522	530
Commercial \| CRE
Financing Receivable, Allowance for Credit Losses [Roll Forward]
ACL, beginning balance	160	145	175
Charge-Offs	(13)	(10)	(9)
Allowance for Loan and Lease Losses, Adjustments, Other	0	0	0
Recoveries	8	16	19
Provision for credit losses	35	9	(40)
ACL, ending balance	190	160	145
Commercial \| Lease financing
Financing Receivable, Allowance for Credit Losses [Roll Forward]
ACL, beginning balance	9	7	5
Charge-Offs	(4)	(5)	(6)
Allowance for Loan and Lease Losses, Adjustments, Other	0	0	0
Recoveries	1	2	2
Provision for credit losses	5	5	6
ACL, ending balance	11	9	7
Retail \| Residential mortgage
Financing Receivable, Allowance for Credit Losses [Roll Forward]
ACL, beginning balance	209	227	217
Charge-Offs	(21)	(47)	(40)
Allowance for Loan and Lease Losses, Adjustments, Other	0	0	0
Recoveries	2	2	3
Provision for credit losses	42	27	47
ACL, ending balance	232	209	227
Retail \| Direct
Financing Receivable, Allowance for Credit Losses [Roll Forward]
ACL, beginning balance	106	103	105
Charge-Offs	(71)	(61)	(53)
Allowance for Loan and Lease Losses, Adjustments, Other	0	0	0
Recoveries	23	25	26
Provision for credit losses	39	39	25
ACL, ending balance	97	106	103
Retail \| Indirect
Financing Receivable, Allowance for Credit Losses [Roll Forward]
ACL, beginning balance	348	327	305
Charge-Offs	(391)	(402)	(366)
Allowance for Loan and Lease Losses, Adjustments, Other	0	0	0
Recoveries	62	60	55
Provision for credit losses	337	363	333
ACL, ending balance	356	348	327
Revolving credit
Financing Receivable, Allowance for Credit Losses [Roll Forward]
ACL, beginning balance	108	106	104
Charge-Offs	(84)	(76)	(69)
Allowance for Loan and Lease Losses, Adjustments, Other	0	0	0
Recoveries	19	19	20
Provision for credit losses	74	59	51
ACL, ending balance	117	108	106
PCI
Financing Receivable, Allowance for Credit Losses [Roll Forward]
ACL, beginning balance	28	44	61
Charge-Offs	(2)	(1)	(15)
Allowance for Loan and Lease Losses, Adjustments, Other	0	0	0
Recoveries	0	0	0
Provision for credit losses	(17)	(15)	(2)
ACL, ending balance	9	28	44
ALLL
Financing Receivable, Allowance for Credit Losses [Roll Forward]
ACL, beginning balance	1,490	1,489	1,460
Charge-Offs	(678)	(697)	(701)
Allowance for Loan and Lease Losses, Adjustments, Other	0	0	0
Recoveries	154	160	169
Provision for credit losses	592	538	561
ACL, ending balance	1,558	1,490	1,489
RUFC
Financing Receivable, Allowance for Credit Losses [Roll Forward]
ACL, beginning balance	119	110	90
Charge-Offs	0	0	0
Allowance for Loan and Lease Losses, Adjustments, Other	0	0	9
Recoveries	0	0	0
Provision for credit losses	(26)	9	11
ACL, ending balance	93	119	110
ACL
Financing Receivable, Allowance for Credit Losses [Roll Forward]
ACL, beginning balance	1,609	1,599	1,550
Charge-Offs	(678)	(697)	(701)
Allowance for Loan and Lease Losses, Adjustments, Other	0	0	9
Recoveries	154	160	169
Provision for credit losses	566	547	572
ACL, ending balance	$ 1,651	$ 1,609	$ 1,599

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 other addition (reduction) in allowance reserve for credit loss.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
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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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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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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
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-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

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-Topic 942
-SubTopic 220
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-URI http://asc.fasb.org/extlink&oid=114873765&loc=SL114874048-224260

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
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-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585

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