Asset Quality - Breakdown of Allowance for Loan and Lease Losses and Corresponding Loan Balances (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment, Allowance, Total ALLL - Including Discontinued Operations	$ 32	$ 26
Collectively Evaluated for Impairment, Allowance, Total ALLL - Including Discontinued Operations	863	861
Purchased Credit Impaired, Allowance, Total ALLL - Including Discontinued Operations	6	6
Loans, Outstanding, Total ALLL - Including Discontinued Operations	90,398	87,719
Individually Evaluated for Impairment, Outstanding, Total ALLL - Including Discontinued Operations	548	375
Collectively Evaluated for Impairment, Outstanding, Total ALLL - Including Discontinued Operations	89,244	86,606
Purchased Credit Impaired, Outstanding, Total ALLL - Including Discontinued Operations	606	738
Continuing Operations [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment, Allowance	30	23
Collectively Evaluated for Impairment, Allowance	851	848
Purchase Credit Impairment, Allowance	6	6
Total loans	89,268	86,405
Individually Evaluated for Impairment, Outstanding	526	354
Collectively Evaluated for Impairment, Outstanding	88,136	85,313
Purchase Credit Impairment, Outstanding	606	738
Continuing Operations [Member] | Commercial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment, Allowance	16	6
Collectively Evaluated for Impairment, Allowance	733	724
Purchase Credit Impairment, Allowance	5	5
Total loans	65,972	62,733
Individually Evaluated for Impairment, Outstanding	308	148
Collectively Evaluated for Impairment, Outstanding	65,403	62,228
Purchase Credit Impairment, Outstanding	261	357
Continuing Operations [Member] | Consumer Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment, Allowance	14	17
Collectively Evaluated for Impairment, Allowance	118	124
Purchase Credit Impairment, Allowance	1	1
Total loans	23,296	23,672
Individually Evaluated for Impairment, Outstanding	218	206
Collectively Evaluated for Impairment, Outstanding	22,733	23,085
Purchase Credit Impairment, Outstanding	345	381
Discontinued Operations [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment, Allowance	2	3
Collectively Evaluated for Impairment, Allowance	12	13
Purchase Credit Impairment, Allowance	0	0
Total loans	1,130	1,314
Individually Evaluated for Impairment, Outstanding	22	21
Collectively Evaluated for Impairment, Outstanding	1,108	1,293
Purchase Credit Impairment, Outstanding	0	0
Commercial and Industrial [Member] | Continuing Operations [Member] | Commercial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment, Allowance	5	6
Collectively Evaluated for Impairment, Allowance	536	520
Purchase Credit Impairment, Allowance	2	3
Total loans	45,023	41,859
Individually Evaluated for Impairment, Outstanding	232	136
Collectively Evaluated for Impairment, Outstanding	44,737	41,640
Purchase Credit Impairment, Outstanding	54	83
Commercial Real Estate: Commercial Mortgage [Member] | Continuing Operations [Member] | Commercial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment, Allowance	11	0
Collectively Evaluated for Impairment, Allowance	129	131
Purchase Credit Impairment, Allowance	3	2
Total loans	14,716	14,088
Individually Evaluated for Impairment, Outstanding	76	12
Collectively Evaluated for Impairment, Outstanding	14,436	13,828
Purchase Credit Impairment, Outstanding	204	248
Commercial Real Estate: Construction [Member] | Continuing Operations [Member] | Commercial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment, Allowance	0	0
Collectively Evaluated for Impairment, Allowance	31	30
Purchase Credit Impairment, Allowance	0	0
Total loans	1,763	1,960
Individually Evaluated for Impairment, Outstanding	0	0
Collectively Evaluated for Impairment, Outstanding	1,760	1,934
Purchase Credit Impairment, Outstanding	3	26
Commercial Real Estate Loans [Member] | Continuing Operations [Member] | Commercial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment, Allowance	11	0
Collectively Evaluated for Impairment, Allowance	160	161
Purchase Credit Impairment, Allowance	3	2
Total loans	16,479	16,048
Individually Evaluated for Impairment, Outstanding	76	12
Collectively Evaluated for Impairment, Outstanding	16,196	15,762
Purchase Credit Impairment, Outstanding	207	274
Commercial Lease Financing [Member] | Continuing Operations [Member] | Commercial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment, Allowance	0	0
Collectively Evaluated for Impairment, Allowance	37	43
Purchase Credit Impairment, Allowance	0	0
Total loans	4,470	4,826
Individually Evaluated for Impairment, Outstanding	0	0
Collectively Evaluated for Impairment, Outstanding	4,470	4,826
Purchase Credit Impairment, Outstanding	0	0
Real Estate - Residential Mortgage [Member] | Continuing Operations [Member] | Consumer Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment, Allowance	4	5
Collectively Evaluated for Impairment, Allowance	5	2
Purchase Credit Impairment, Allowance	0	0
Total loans	5,497	5,483
Individually Evaluated for Impairment, Outstanding	49	49
Collectively Evaluated for Impairment, Outstanding	5,125	5,079
Purchase Credit Impairment, Outstanding	323	355
Home Equity Loans [Member] | Continuing Operations [Member] | Consumer Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment, Allowance	7	9
Collectively Evaluated for Impairment, Allowance	26	33
Purchase Credit Impairment, Allowance	1	1
Total loans	11,339	12,028
Individually Evaluated for Impairment, Outstanding	127	117
Collectively Evaluated for Impairment, Outstanding	11,193	11,889
Purchase Credit Impairment, Outstanding	19	22
Consumer Direct Loans [Member] | Continuing Operations [Member] | Consumer Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment, Allowance	0	0
Collectively Evaluated for Impairment, Allowance	26	28
Purchase Credit Impairment, Allowance	0	0
Total loans	1,807	1,794
Individually Evaluated for Impairment, Outstanding	4	4
Collectively Evaluated for Impairment, Outstanding	1,800	1,786
Purchase Credit Impairment, Outstanding	3	4
Consumer Credit Card Financing Receivable [Member] | Continuing Operations [Member] | Consumer Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment, Allowance	0	0
Collectively Evaluated for Impairment, Allowance	45	44
Purchase Credit Impairment, Allowance	0	0
Total loans	1,098	1,106
Individually Evaluated for Impairment, Outstanding	3	2
Collectively Evaluated for Impairment, Outstanding	1,095	1,104
Purchase Credit Impairment, Outstanding	0	0
Consumer Indirect Loans [Member] | Continuing Operations [Member] | Consumer Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment, Allowance	3	3
Collectively Evaluated for Impairment, Allowance	16	17
Purchase Credit Impairment, Allowance	0	0
Total loans	3,555	3,261
Individually Evaluated for Impairment, Outstanding	35	34
Collectively Evaluated for Impairment, Outstanding	3,520	3,227
Purchase Credit Impairment, Outstanding	0	0
Education Lending [Member] | Discontinued Operations [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans at fair value	$ 2	$ 2