Asset Quality - Changes in Allowance for Loan and Lease Losses by Loan Category (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	$ 893	$ 882	$ 882
Provision	60	73
Charge-offs	(76)	(83)
Recoveries	20	21
Ending balance	897	893	893
Provision (credit) for losses on lending-related commitments	3	(7)
Continuing Operations [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	877	858	858
Provision	58	70
Charge-offs	(72)	(77)
Recoveries	18	19
Ending balance	881	870	877
Continuing Operations [Member] | Commercial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	735	716	716
Provision	38	42
Charge-offs	(39)	(39)
Recoveries	8	8
Ending balance	742	727	735
Continuing Operations [Member] | Commercial and Industrial [Member] | Commercial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	529	508	508
Provision	35	31
Charge-offs	(37)	(32)
Recoveries	6	5
Ending balance	533	512	529
Continuing Operations [Member] | Commercial Real Estate: Commercial Mortgage [Member] | Commercial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	133	144	144
Provision	4	2
Charge-offs	(1)	0
Recoveries	0	0
Ending balance	136	146	133
Continuing Operations [Member] | RE Construction [Member] | Commercial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	30	22	22
Provision	2	6
Charge-offs	0	0
Recoveries	1	1
Ending balance	33	29	30
Continuing Operations [Member] | Commercial Real Estate [Member] | Commercial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	163	166	166
Provision	6	8
Charge-offs	(1)	0
Recoveries	1	1
Ending balance	169	175	163
Continuing Operations [Member] | Commercial Lease Financing [Member] | Commercial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	43	42	42
Provision	(3)	3
Charge-offs	(1)	(7)
Recoveries	1	2
Ending balance	40	40	43
Continuing Operations [Member] | Real Estate - Residential Mortgage [Member] | Consumer Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	7	17	17
Provision	3	(3)
Charge-offs	(1)	2
Recoveries	0	2
Ending balance	9	18	7
Continuing Operations [Member] | Home Equity Loans [Member] | Consumer Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	43	54	54
Provision	(4)	4
Charge-offs	(4)	(8)
Recoveries	3	3
Ending balance	38	53	43
Continuing Operations [Member] | Consumer Direct Loans [Member] | Consumer Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	28	24	24
Provision	5	9
Charge-offs	(8)	(10)
Recoveries	2	1
Ending balance	27	24	28
Continuing Operations [Member] | Credit Cards [Member] | Consumer Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	44	38	38
Provision	12	10
Charge-offs	(12)	(11)
Recoveries	1	1
Ending balance	45	38	44
Continuing Operations [Member] | Consumer Indirect Loans [Member] | Consumer Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	20	9	9
Provision	4	8
Charge-offs	(8)	(11)
Recoveries	4	4
Ending balance	20	10	20
Continuing Operations [Member] | Consumer Loans [Member] | Consumer Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	142	142	142
Provision	20	28
Charge-offs	(33)	(38)
Recoveries	10	11
Ending balance	139	143	142
Discontinued Operations [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	16	24	24
Provision	2	3
Charge-offs	(4)	(6)
Recoveries	2	2
Ending balance	$ 16	$ 23	$ 16