Asset Quality - Changes in Allowance for Loan and Lease Losses by Loan Category (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	$ 897	$ 893	$ 882
Provision	444	248	237
Charge-offs	(511)	(339)	(328)
Recoveries	80	95	102
Ending balance	910	897	893
Provision for credit losses	445	246	229
Realization of loss related to previously disclosed fraud incident	139
Continuing Operations [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	883	877	858
Provision	441	240	227
Charge-offs	(499)	(324)	(302)
Recoveries	75	90	94
Ending balance	900	883	877
Provision for credit losses	4	6	2
Discontinued Operations [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	14	16	24
Provision	3	8	10
Charge-offs	(12)	(15)	(26)
Recoveries	5	5	8
Ending balance	10	14	16
Commercial Loans [Member] | Continuing Operations [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	743	735	716
Provision	332	151	130
Charge-offs	(358)	(190)	(160)
Recoveries	34	47	49
Ending balance	751	743	735
Commercial Loans [Member] | Continuing Operations [Member] | Commercial, Financial and Agricultural [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	532	529	508
Provision	311	125	114
Charge-offs	(319)	(159)	(133)
Recoveries	27	37	40
Ending balance	551	532	529
Commercial Loans [Member] | Continuing Operations [Member] | Commercial Real Estate: Commercial Mortgage [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	142	133	144
Provision	7	27	(2)
Charge-offs	(8)	(21)	(11)
Recoveries	2	3	2
Ending balance	143	142	133
Commercial Loans [Member] | Continuing Operations [Member] | Commercial Real Estate Construction Financing Receivable [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	33	30	22
Provision	(6)	1	9
Charge-offs	(5)	0	(2)
Recoveries	0	2	1
Ending balance	22	33	30
Commercial Loans [Member] | Continuing Operations [Member] | Commercial Lease Financing [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	36	43	42
Provision	20	(2)	9
Charge-offs	(26)	(10)	(14)
Recoveries	5	5	6
Ending balance	35	36	43
Consumer Loans [Member] | Continuing Operations [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	140	142	142
Provision	109	89	97
Charge-offs	(141)	(134)	(142)
Recoveries	41	43	45
Ending balance	149	140	142
Consumer Loans [Member] | Continuing Operations [Member] | Real Estate - Residential Mortgage [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	7	7	17
Provision	1	1	(11)
Charge-offs	(3)	(3)	(3)
Recoveries	2	2	4
Ending balance	7	7	7
Consumer Loans [Member] | Continuing Operations [Member] | Home Equity Loan [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	35	43	54
Provision	7	2	4
Charge-offs	(19)	(21)	(30)
Recoveries	8	11	15
Ending balance	31	35	43
Consumer Loans [Member] | Continuing Operations [Member] | Consumer Direct Loans [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	30	28	24
Provision	38	31	32
Charge-offs	(41)	(36)	(34)
Recoveries	7	7	6
Ending balance	34	30	28
Consumer Loans [Member] | Continuing Operations [Member] | Consumer Credit Card [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	48	44	38
Provision	36	41	45
Charge-offs	(44)	(44)	(44)
Recoveries	7	7	5
Ending balance	47	48	44
Consumer Loans [Member] | Continuing Operations [Member] | Consumer Indirect Loans [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	20	20	9
Provision	27	14	27
Charge-offs	(34)	(30)	(31)
Recoveries	17	16	15
Ending balance	$ 30	$ 20	$ 20