Credit Quality - Summary of the Credit Risk Profile of the Commercial Portfolio Segment by Class (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Financing Receivable, Modifications [Line Items]
Total loans and leases	$ 109,225	$ 95,086
Commercial and Industrial Loans
Financing Receivable, Modifications [Line Items]
Total loans and leases	50,768	44,340
Commercial Mortgage Loans, Owner-occupied
Financing Receivable, Modifications [Line Items]
Total loans and leases	4,768	3,284
Commercial Mortgage Loans, Nonowner-Occupied
Financing Receivable, Modifications [Line Items]
Total loans and leases	6,054	3,690
Commercial Construction Loans
Financing Receivable, Modifications [Line Items]
Total loans and leases	5,281	4,657
Commercial Leases
Financing Receivable, Modifications [Line Items]
Total loans and leases	3,495	3,600
Commercial Portfolio Segment
Financing Receivable, Modifications [Line Items]
Total loans and leases	70,366	59,571
Commercial Portfolio Segment | Commercial and Industrial Loans
Financing Receivable, Modifications [Line Items]
Total loans and leases	50,768	44,340
Commercial Portfolio Segment | Commercial Mortgage Loans, Owner-occupied
Financing Receivable, Modifications [Line Items]
Total loans and leases	4,768	3,284
Commercial Portfolio Segment | Commercial Mortgage Loans, Nonowner-Occupied
Financing Receivable, Modifications [Line Items]
Total loans and leases	6,054	3,690
Commercial Portfolio Segment | Commercial Construction Loans
Financing Receivable, Modifications [Line Items]
Total loans and leases	5,281	4,657
Commercial Portfolio Segment | Commercial Leases
Financing Receivable, Modifications [Line Items]
Total loans and leases	3,495	3,600
Pass | Commercial Portfolio Segment
Financing Receivable, Modifications [Line Items]
Total loans and leases	66,705	57,581
Pass | Commercial Portfolio Segment | Commercial and Industrial Loans
Financing Receivable, Modifications [Line Items]
Total loans and leases	47,944	42,695
Pass | Commercial Portfolio Segment | Commercial Mortgage Loans, Owner-occupied
Financing Receivable, Modifications [Line Items]
Total loans and leases	4,419	3,122
Pass | Commercial Portfolio Segment | Commercial Mortgage Loans, Nonowner-Occupied
Financing Receivable, Modifications [Line Items]
Total loans and leases	5,786	3,632
Pass | Commercial Portfolio Segment | Commercial Construction Loans
Financing Receivable, Modifications [Line Items]
Total loans and leases	5,192	4,657
Pass | Commercial Portfolio Segment | Commercial Leases
Financing Receivable, Modifications [Line Items]
Total loans and leases	3,364	3,475
Special Mention | Commercial Portfolio Segment
Financing Receivable, Modifications [Line Items]
Total loans and leases	1,612	901
Special Mention | Commercial Portfolio Segment | Commercial and Industrial Loans
Financing Receivable, Modifications [Line Items]
Total loans and leases	1,300	779
Special Mention | Commercial Portfolio Segment | Commercial Mortgage Loans, Owner-occupied
Financing Receivable, Modifications [Line Items]
Total loans and leases	152	23
Special Mention | Commercial Portfolio Segment | Commercial Mortgage Loans, Nonowner-Occupied
Financing Receivable, Modifications [Line Items]
Total loans and leases	76	27
Special Mention | Commercial Portfolio Segment | Commercial Construction Loans
Financing Receivable, Modifications [Line Items]
Total loans and leases	42	0
Special Mention | Commercial Portfolio Segment | Commercial Leases
Financing Receivable, Modifications [Line Items]
Total loans and leases	42	72
Substandard | Commercial Portfolio Segment
Financing Receivable, Modifications [Line Items]
Total loans and leases	2,038	1,076
Substandard | Commercial Portfolio Segment | Commercial and Industrial Loans
Financing Receivable, Modifications [Line Items]
Total loans and leases	1,513	853
Substandard | Commercial Portfolio Segment | Commercial Mortgage Loans, Owner-occupied
Financing Receivable, Modifications [Line Items]
Total loans and leases	197	139
Substandard | Commercial Portfolio Segment | Commercial Mortgage Loans, Nonowner-Occupied
Financing Receivable, Modifications [Line Items]
Total loans and leases	192	31
Substandard | Commercial Portfolio Segment | Commercial Construction Loans
Financing Receivable, Modifications [Line Items]
Total loans and leases	47	0
Substandard | Commercial Portfolio Segment | Commercial Leases
Financing Receivable, Modifications [Line Items]
Total loans and leases	89	53
Doubtful | Commercial Portfolio Segment
Financing Receivable, Modifications [Line Items]
Total loans and leases	11	13
Doubtful | Commercial Portfolio Segment | Commercial and Industrial Loans
Financing Receivable, Modifications [Line Items]
Total loans and leases	11	13
Doubtful | Commercial Portfolio Segment | Commercial Mortgage Loans, Owner-occupied
Financing Receivable, Modifications [Line Items]
Total loans and leases	0	0
Doubtful | Commercial Portfolio Segment | Commercial Mortgage Loans, Nonowner-Occupied
Financing Receivable, Modifications [Line Items]
Total loans and leases	0	0
Doubtful | Commercial Portfolio Segment | Commercial Construction Loans
Financing Receivable, Modifications [Line Items]
Total loans and leases	0	0
Doubtful | Commercial Portfolio Segment | Commercial Leases
Financing Receivable, Modifications [Line Items]
Total loans and leases	$ 0	$ 0