Asset Quality - Changes in Allowance for Loan and Lease Losses by Loan Category (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	$ 897	$ 893	$ 893	$ 882	$ 882
Provision	66	66	126	139
Charge-offs	(82)	(86)	(158)	(169)
Recoveries	20	18	40	39
Ending balance	901	891	901	891	893
Provision (credit) for losses on lending-related commitments	(2)	0	1	(7)
Continuing Operations [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	881	870	877	858	858
Provision	66	66	124	136
Charge-offs	(79)	(82)	(151)	(159)
Recoveries	19	16	37	35
Ending balance	887	870	887	870	877
Continuing Operations [Member] | Commercial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	742	727	735	716	716
Provision	44	55	82	97
Charge-offs	(45)	(44)	(84)	(83)
Recoveries	8	2	16	10
Ending balance	749	740	749	740	735
Continuing Operations [Member] | Commercial and Industrial [Member] | Commercial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	533	512	529	508	508
Provision	41	54	76	85
Charge-offs	(39)	(40)	(76)	(72)
Recoveries	7	2	13	7
Ending balance	542	528	542	528	529
Continuing Operations [Member] | Commercial Real Estate: Commercial Mortgage [Member] | Commercial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	136	146	133	144	144
Provision	4	1	8	3
Charge-offs	(2)	(3)	(3)	(3)
Recoveries	1	0	1	0
Ending balance	139	144	139	144	133
Continuing Operations [Member] | RE Construction [Member] | Commercial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	33	29	30	22	22
Provision	(5)	(1)	(3)	5
Charge-offs	0	0	0	0
Recoveries	0	0	1	1
Ending balance	28	28	28	28	30
Continuing Operations [Member] | Commercial Real Estate [Member] | Commercial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	169	175	163	166	166
Provision	(1)	0	5	8
Charge-offs	(2)	(3)	(3)	(3)
Recoveries	1	0	2	1
Ending balance	167	172	167	172	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	4	1	1	4
Charge-offs	(4)	(1)	(5)	(8)
Recoveries	0	0	1	2
Ending balance	40	40	40	40	43
Continuing Operations [Member] | Real Estate - Residential Mortgage [Member] | Consumer Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	9	18	7	17	17
Provision	1	(6)	4	(9)
Charge-offs	0	(4)	(1)	(2)
Recoveries	0	1	0	3
Ending balance	10	9	10	9	7
Continuing Operations [Member] | Home Equity Loans [Member] | Consumer Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	38	53	43	54	54
Provision	2	(7)	(2)	(3)
Charge-offs	(6)	(9)	(10)	(17)
Recoveries	3	5	6	8
Ending balance	37	42	37	42	43
Continuing Operations [Member] | Consumer Direct Loans [Member] | Consumer Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	27	24	28	24	24
Provision	6	7	11	16
Charge-offs	(9)	(8)	(17)	(18)
Recoveries	2	2	4	3
Ending balance	26	25	26	25	28
Continuing Operations [Member] | Credit Cards [Member] | Consumer Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	45	38	44	38	38
Provision	11	16	23	26
Charge-offs	(12)	(12)	(24)	(23)
Recoveries	2	2	3	3
Ending balance	46	44	46	44	44
Continuing Operations [Member] | Consumer Indirect Loans [Member] | Consumer Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	20	10	20	9	9
Provision	2	1	6	9
Charge-offs	(7)	(5)	(15)	(16)
Recoveries	4	4	8	8
Ending balance	19	10	19	10	20
Continuing Operations [Member] | Consumer Loans [Member] | Consumer Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	139	143	142	142	142
Provision	22	11	42	39
Charge-offs	(34)	(38)	(67)	(76)
Recoveries	11	14	21	25
Ending balance	138	130	138	130	142
Discontinued Operations [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	16	23	16	24	24
Provision	0	0	2	3
Charge-offs	(3)	(4)	(7)	(10)
Recoveries	1	2	3	4
Ending balance	$ 14	$ 21	$ 14	$ 21	$ 16