Asset Quality - Changes in Allowance for Loan and Lease Losses by Loan Category (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	$ 893	$ 882	$ 824
Provision	248	237	280
Charge-offs	(339)	(328)	(289)
Recoveries	95	102	67
Ending balance	897	893	882
Provision for credit losses	246	229	266
Continuing Operations [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	877	858	796
Provision	240	227	267
Charge-offs	(324)	(302)	(261)
Recoveries	90	94	56
Ending balance	883	877	858
Provision for credit losses	6	2	1
Discontinued Operations [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	16	24	28
Provision	8	10	13
Charge-offs	(15)	(26)	(28)
Recoveries	5	8	11
Ending balance	14	16	24
Commercial Loans [Member] \| Continuing Operations [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	735	716	656
Provision	151	130	179
Charge-offs	(190)	(160)	(144)
Recoveries	47	49	25
Ending balance	743	735	716
Commercial Loans [Member] \| Continuing Operations [Member] \| Commercial, Financial and Agricultural [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	529	508	450
Provision	125	114	165
Charge-offs	(159)	(133)	(118)
Recoveries	37	40	11
Ending balance	532	529	508
Commercial Loans [Member] \| Continuing Operations [Member] \| Commercial Real Estate: Commercial Mortgage [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	133	144	134
Provision	27	(2)	6
Charge-offs	(21)	(11)	(5)
Recoveries	3	2	9
Ending balance	142	133	144
Commercial Loans [Member] \| Continuing Operations [Member] \| Commercial Real Estate Construction Financing Receivable [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	30	22	25
Provision	1	9	4
Charge-offs	0	(2)	(9)
Recoveries	2	1	2
Ending balance	33	30	22
Commercial Loans [Member] \| Continuing Operations [Member] \| Commercial Lease Financing [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	43	42	47
Provision	(2)	9	4
Charge-offs	(10)	(14)	(12)
Recoveries	5	6	3
Ending balance	36	43	42
Consumer Loans [Member] \| Continuing Operations [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	142	142	140
Provision	89	97	88
Charge-offs	(134)	(142)	(117)
Recoveries	43	45	31
Ending balance	140	142	142
Consumer Loans [Member] \| Continuing Operations [Member] \| Real Estate - Residential Mortgage [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	7	17	18
Provision	1	(11)	2
Charge-offs	(3)	(3)	(4)
Recoveries	2	4	1
Ending balance	7	7	17
Consumer Loans [Member] \| Continuing Operations [Member] \| Home Equity Loan [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	43	54	57
Provision	2	4	13
Charge-offs	(21)	(30)	(30)
Recoveries	11	15	14
Ending balance	35	43	54
Consumer Loans [Member] \| Continuing Operations [Member] \| Consumer Direct Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	28	24	20
Provision	31	32	26
Charge-offs	(36)	(34)	(27)
Recoveries	7	6	5
Ending balance	30	28	24
Consumer Loans [Member] \| Continuing Operations [Member] \| Consumer Credit Card [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	44	38	32
Provision	41	45	37
Charge-offs	(44)	(44)	(35)
Recoveries	7	5	4
Ending balance	48	44	38
Consumer Loans [Member] \| Continuing Operations [Member] \| Consumer Indirect Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	20	9	13
Provision	14	27	10
Charge-offs	(30)	(31)	(21)
Recoveries	16	15	7
Ending balance	$ 20	$ 20	$ 9

Financing receivable allowance for credit losses lending related commitments.

No definition available.

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- Definition

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

+ 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)(1)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

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- Definition

Amount of recovery of financing receivables doubtful of collection that were previously charged off.

+ 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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- Definition

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 direct write-downs of financing receivables charged against the allowance.

+ 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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- Definition

Amount of expense related to estimated loss from loan and lease transactions.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
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-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
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-URI http://asc.fasb.org/extlink&oid=114873765&loc=SL114874048-224260

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