Credit Quality - Recorded Investment in Portfolio Loans and Leases by Age and Class (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current Loans and Leases	$ 108,417	$ 94,487
Total Past Due	808	599
Total portfolio loans and leases	109,225	95,086
90-Days past Due and Still Accruing	132	93
30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	440	326
90 Days and Greater Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	368	273
Commercial and Industrial Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current Loans and Leases	50,504	44,213
Total Past Due	264	127
Total portfolio loans and leases	50,768	44,340
90-Days past Due and Still Accruing	15	4
Commercial and Industrial Loans | 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	131	32
Commercial and Industrial Loans | 90 Days and Greater Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	133	95
Commercial Mortgage Loans, Owner-occupied
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current Loans and Leases	4,742	3,277
Total Past Due	26	7
Total portfolio loans and leases	4,768	3,284
90-Days past Due and Still Accruing	3	2
Commercial Mortgage Loans, Owner-occupied | 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	9	1
Commercial Mortgage Loans, Owner-occupied | 90 Days and Greater Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	17	6
Commercial Mortgage Loans, Nonowner-Occupied
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current Loans and Leases	6,025	3,688
Total Past Due	29	2
Total portfolio loans and leases	6,054	3,690
90-Days past Due and Still Accruing	15	0
Commercial Mortgage Loans, Nonowner-Occupied | 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	13	1
Commercial Mortgage Loans, Nonowner-Occupied | 90 Days and Greater Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	16	1
Commercial construction loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current Loans and Leases	5,280	4,657
Total Past Due	1	0
Total portfolio loans and leases	5,281	4,657
90-Days past Due and Still Accruing	1	0
Commercial construction loans | 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Commercial construction loans | 90 Days and Greater Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1	0
Commercial Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current Loans and Leases	3,479	3,597
Total Past Due	16	3
Total portfolio loans and leases	3,495	3,600
90-Days past Due and Still Accruing	1	0
Commercial Leases | 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2	1
Commercial Leases | 90 Days and Greater Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	14	2
Residential Mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current Loans and Leases	16,390	15,227
Total Past Due	101	98
Total portfolio loans and leases	16,491	15,325
90-Days past Due and Still Accruing	48	38
Residential Mortgage | 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	32	37
Residential Mortgage | 90 Days and Greater Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	69	61
Home Equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current Loans and Leases	6,097	6,280
Total Past Due	121	122
Total portfolio loans and leases	6,218	6,402
90-Days past Due and Still Accruing	0	0
Home Equity | 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	63	71
Home Equity | 90 Days and Greater Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	58	51
Indirect secured consumer loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current Loans and Leases	10,892	8,844
Total Past Due	134	132
Total portfolio loans and leases	11,026	8,976
90-Days past Due and Still Accruing	10	12
Indirect secured consumer loans | 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	120	119
Indirect secured consumer loans | 90 Days and Greater Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	14	13
Credit Card
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current Loans and Leases	2,375	2,381
Total Past Due	92	89
Total portfolio loans and leases	2,467	2,470
90-Days past Due and Still Accruing	38	37
Credit Card | 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	49	47
Credit Card | 90 Days and Greater Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	43	42
Other consumer loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current Loans and Leases	2,633	2,323
Total Past Due	24	19
Total portfolio loans and leases	2,657	2,342
90-Days past Due and Still Accruing	1	0
Other consumer loans | 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	21	17
Other consumer loans | 90 Days and Greater Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 3	$ 2