Asset Quality - Changes in Allowance for Loan and Lease Losses by Loan Category (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	$ 824	$ 823	$ 887
Provision	280	165	80
Charge-offs	(289)	(238)	(256)
Recoveries	67	74	112
Ending balance	882	824	823
Provision for credit losses	266	166	57
Continuing Operations [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	796	794	848
Provision	267	144	59
Charge-offs	(261)	(203)	(211)
Recoveries	56	61	98
Ending balance	858	796	794
Provision for credit losses	1	21
Foreign currency translation adjustment		1	2
Discontinued Operations [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	28	29	39
Provision	13	21	21
Charge-offs	(28)	(35)	(45)
Recoveries	11	13	14
Ending balance	24	28	29
Commercial Loans [Member] | Continuing Operations [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	656	623	621
Ending balance		656	623
Commercial Loans [Member] | Continuing Operations [Member] | Commercial, Financial and Agricultural [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	450	391	362
Provision	165	120	41
Charge-offs	(118)	(77)	(45)
Recoveries	11	16	33
Ending balance	508	450	391
Commercial Loans [Member] | Continuing Operations [Member] | Commercial Real Estate: Commercial Mortgage [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	134	148	165
Provision	6	(16)	(15)
Charge-offs	(5)	(4)	(6)
Recoveries	9	6	4
Ending balance	144	134	148
Commercial Loans [Member] | Continuing Operations [Member] | Commercial Real Estate Construction Financing Receivable [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	25	28	32
Provision	4	(3)	(16)
Charge-offs	(9)	(1)	(5)
Recoveries	2	1	17
Ending balance	22	25	28
Commercial Loans [Member] | Continuing Operations [Member] | Commercial Lease Financing [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	47	56	62
Provision	4	(5)	(6)
Charge-offs	(12)	(11)	(10)
Recoveries	3	7	10
Ending balance	42	47	56
Commercial Loans [Member] | Continuing Operations [Member] | Commercial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	656	623
Provision	179	96	4
Charge-offs	(144)	(93)	(66)
Recoveries	25	30	64
Ending balance	716	656	623
Consumer Loans [Member] | Continuing Operations [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	140	171	227
Ending balance		140	171
Consumer Loans [Member] | Continuing Operations [Member] | Real Estate - Residential Mortgage [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	18	23	37
Provision	2	(2)	(6)
Charge-offs	(4)	(6)	(10)
Recoveries	1	3	2
Ending balance	17	18	23
Consumer Loans [Member] | Continuing Operations [Member] | Home Equity Loan [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	57	71	95
Provision	13	7	8
Charge-offs	(30)	(32)	(46)
Recoveries	14	11	14
Ending balance	54	57	71
Consumer Loans [Member] | Continuing Operations [Member] | Consumer Direct Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	20	22	29
Provision	26	16	17
Charge-offs	(27)	(24)	(30)
Recoveries	5	6	6
Ending balance	24	20	22
Consumer Loans [Member] | Continuing Operations [Member] | Consumer Credit Card [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	32	33	34
Provision	37	27	32
Charge-offs	(35)	(30)	(34)
Recoveries	4	2	1
Ending balance	38	32	33
Consumer Loans [Member] | Continuing Operations [Member] | Consumer Indirect Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	13	22	32
Provision	10	0	4
Charge-offs	(21)	(18)	(25)
Recoveries	7	9	11
Ending balance	9	13	22
Consumer Loans [Member] | Continuing Operations [Member] | Consumer Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	140	171
Provision	88	48	55
Charge-offs	(117)	(110)	(145)
Recoveries	31	31	34
Ending balance	$ 142	$ 140	$ 171