Asset Quality - Changes in Allowance for Loan and Lease Losses by Loan Category (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	$ 891	$ 874	$ 882	$ 824	$ 824
Provision	47	56	186	205
Charge-offs	(81)	(61)	(250)	(200)
Recoveries	41	14	80	54
Ending balance	898	883	898	883	882
Provision (credit) for losses on lending-related commitments	9	3	2	(3)
Foreign currency translation adjustment		1		1
Continuing Operations [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	870	854	858	796	796
Provision	42	55	178	202
Charge-offs	(71)	(55)	(230)	(179)
Recoveries	39	11	74	46
Ending balance	880	865	880	865	858
Continuing Operations [Member] | Commercial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	740	710	716	656	656
Provision	11	35	108	142
Charge-offs	(38)	(31)	(121)	(101)
Recoveries	29	4	39	21
Ending balance	742	718	742	718	716
Continuing Operations [Member] | Commercial and Industrial [Member] | Commercial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	528	513	508	450	450
Provision	8	19	93	137
Charge-offs	(29)	(17)	(101)	(78)
Recoveries	25	2	32	8
Ending balance	532	517	532	517	508
Continuing Operations [Member] | Commercial Real Estate: Commercial Mortgage [Member] | Commercial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	144	135	144	134	134
Provision	(1)	3	2	(1)
Charge-offs	(6)	0	(9)	(3)
Recoveries	1	1	1	9
Ending balance	138	139	138	139	144
Continuing Operations [Member] | RE Construction [Member] | Commercial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	28	17	22	25	25
Provision	3	8	8	(1)
Charge-offs	(2)	(9)	(2)	(9)
Recoveries	0	1	1	2
Ending balance	29	17	29	17	22
Continuing Operations [Member] | Commercial Real Estate [Member] | Commercial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	172	152	166	159	159
Provision	2	11	10	(2)
Charge-offs	(8)	(9)	(11)	(12)
Recoveries	1	2	2	11
Ending balance	167	156	167	156	166
Continuing Operations [Member] | Commercial Lease Financing [Member] | Commercial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	40	45	42	47	47
Provision	1	5	5	7
Charge-offs	(1)	(5)	(9)	(11)
Recoveries	3	0	5	2
Ending balance	43	45	43	45	42
Continuing Operations [Member] | Real Estate - Residential Mortgage [Member] | Consumer Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	9	18	17	18	18
Provision	(2)	(3)	(11)	(2)
Charge-offs	0	(1)	(2)	(4)
Recoveries	1	1	4	3
Ending balance	8	15	8	15	17
Continuing Operations [Member] | Home Equity Loans [Member] | Consumer Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	42	65	54	57	57
Provision	(1)	1	(4)	19
Charge-offs	(6)	(5)	(23)	(22)
Recoveries	4	3	12	10
Ending balance	39	64	39	64	54
Continuing Operations [Member] | Consumer Direct Loans [Member] | Consumer Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	25	19	24	20	20
Provision	10	4	26	12
Charge-offs	(8)	(6)	(26)	(18)
Recoveries	1	1	4	4
Ending balance	28	18	28	18	24
Continuing Operations [Member] | Credit Cards [Member] | Consumer Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	44	30	38	32	32
Provision	10	17	36	29
Charge-offs	(11)	(9)	(34)	(25)
Recoveries	1	1	4	3
Ending balance	44	39	44	39	38
Continuing Operations [Member] | Consumer Indirect Loans [Member] | Consumer Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	10	12	9	13	13
Provision	14	1	23	2
Charge-offs	(8)	(3)	(24)	(9)
Recoveries	3	1	11	5
Ending balance	19	11	19	11	9
Continuing Operations [Member] | Consumer Loans [Member] | Consumer Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	130	144	142	140	140
Provision	31	20	70	60
Charge-offs	(33)	(24)	(109)	(78)
Recoveries	10	7	35	25
Ending balance	138	147	138	147	142
Discontinued Operations [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	21	20	24	28	28
Provision	5	1	8	3
Charge-offs	(10)	(6)	(20)	(21)
Recoveries	2	3	6	8
Ending balance	$ 18	$ 18	$ 18	$ 18	$ 24