Asset Quality - Changes in Allowance for Loan and Lease Losses by Loan Category (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	$ 901	$ 891	$ 893	$ 882	$ 882
Provision	63	47	189	186
Charge-offs	(85)	(81)	(243)	(250)
Recoveries	22	41	62	80
Ending balance	901	898	901	898	893
Provision (credit) for losses on lending-related commitments	2	9	3	2
Continuing Operations [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	887	870	877	858	858
Provision	60	42	184	178
Charge-offs	(81)	(71)	(232)	(230)
Recoveries	21	39	58	74
Ending balance	887	880	887	880	877
Continuing Operations [Member] | Commercial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	749	740	735	716	716
Provision	44	11	126	108
Charge-offs	(48)	(38)	(132)	(121)
Recoveries	9	29	25	39
Ending balance	754	742	754	742	735
Continuing Operations [Member] | Commercial and Industrial [Member] | Commercial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	542	528	529	508	508
Provision	34	8	110	93
Charge-offs	(38)	(29)	(114)	(101)
Recoveries	5	25	18	32
Ending balance	543	532	543	532	529
Continuing Operations [Member] | Commercial Real Estate: Commercial Mortgage [Member] | Commercial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	139	144	133	144	144
Provision	9	(1)	17	2
Charge-offs	(6)	(6)	(9)	(9)
Recoveries	1	1	2	1
Ending balance	143	138	143	138	133
Continuing Operations [Member] | RE Construction [Member] | Commercial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	28	28	30	22	22
Provision	3	3	0	8
Charge-offs	0	(2)	0	(2)
Recoveries	0	0	1	1
Ending balance	31	29	31	29	30
Continuing Operations [Member] | Commercial Real Estate [Member] | Commercial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	167	172	163	166	166
Provision	12	2	17	10
Charge-offs	(6)	(8)	(9)	(11)
Recoveries	1	1	3	2
Ending balance	174	167	174	167	163
Continuing Operations [Member] | Commercial Lease Financing [Member] | Commercial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	40	40	43	42	42
Provision	(2)	1	(1)	5
Charge-offs	(4)	(1)	(9)	(9)
Recoveries	3	3	4	5
Ending balance	37	43	37	43	43
Continuing Operations [Member] | Real Estate - Residential Mortgage [Member] | Consumer Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	10	9	7	17	17
Provision	(1)	(2)	3	(11)
Charge-offs	(2)	0	(3)	(2)
Recoveries	2	1	2	4
Ending balance	9	8	9	8	7
Continuing Operations [Member] | Home Equity Loans [Member] | Consumer Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	37	42	43	54	54
Provision	(2)	(1)	(4)	(4)
Charge-offs	(4)	(6)	(14)	(23)
Recoveries	3	4	9	12
Ending balance	34	39	34	39	43
Continuing Operations [Member] | Consumer Direct Loans [Member] | Consumer Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	26	25	28	24	24
Provision	9	10	20	26
Charge-offs	(10)	(8)	(27)	(26)
Recoveries	1	1	5	4
Ending balance	26	28	26	28	28
Continuing Operations [Member] | Credit Cards [Member] | Consumer Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	46	44	44	38	38
Provision	7	10	30	36
Charge-offs	(10)	(11)	(34)	(34)
Recoveries	2	1	5	4
Ending balance	45	44	45	44	44
Continuing Operations [Member] | Consumer Indirect Loans [Member] | Consumer Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	19	10	20	9	9
Provision	3	14	9	23
Charge-offs	(7)	(8)	(22)	(24)
Recoveries	4	3	12	11
Ending balance	19	19	19	19	20
Continuing Operations [Member] | Consumer Loans [Member] | Consumer Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	138	130	142	142	142
Provision	16	31	58	70
Charge-offs	(33)	(33)	(100)	(109)
Recoveries	12	10	33	35
Ending balance	133	138	133	138	142
Discontinued Operations [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	14	21	16	24	24
Provision	3	5	5	8
Charge-offs	(4)	(10)	(11)	(20)
Recoveries	1	2	4	6
Ending balance	$ 14	$ 18	$ 14	$ 18	$ 16