Loans and Leases - Summary of Commercial Loans and Leases by Credit Quality (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	$ 23,289	$ 22,153
Total commercial loans and leases
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	14,721	13,761
Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	8,960	8,786
Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	5,308	4,556
Commercial leases
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	432	373
Other
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	21	46
Originated Loans and Leases
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	20,397	18,062
Originated Loans and Leases | Total commercial loans and leases
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	12,630	10,730
Originated Loans and Leases | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	7,114	6,171
Originated Loans and Leases | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	5,063	4,140
Originated Loans and Leases | Commercial leases
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	432	373
Originated Loans and Leases | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	21	46
Loans Acquired in a Business Combination
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	2,892	4,091
Loans Acquired in a Business Combination | Total commercial loans and leases
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	2,091	3,031
Loans Acquired in a Business Combination | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	1,846	2,615
Loans Acquired in a Business Combination | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	245	416
Pass | Originated Loans and Leases | Total commercial loans and leases
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	12,032	10,173
Pass | Originated Loans and Leases | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	6,821	5,883
Pass | Originated Loans and Leases | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	4,768	3,879
Pass | Originated Loans and Leases | Commercial leases
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	423	366
Pass | Originated Loans and Leases | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	20	45
Pass | Loans Acquired in a Business Combination | Total commercial loans and leases
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	1,804	2,611
Pass | Loans Acquired in a Business Combination | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	1,603	2,256
Pass | Loans Acquired in a Business Combination | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	201	355
Special Mention | Originated Loans and Leases | Total commercial loans and leases
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	323	344
Special Mention | Originated Loans and Leases | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	171	163
Special Mention | Originated Loans and Leases | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	149	180
Special Mention | Originated Loans and Leases | Commercial leases
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	3	1
Special Mention | Originated Loans and Leases | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	0	0
Special Mention | Loans Acquired in a Business Combination | Total commercial loans and leases
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	135	186
Special Mention | Loans Acquired in a Business Combination | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	116	168
Special Mention | Loans Acquired in a Business Combination | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	19	18
Substandard | Originated Loans and Leases | Total commercial loans and leases
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	272	213
Substandard | Originated Loans and Leases | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	121	125
Substandard | Originated Loans and Leases | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	144	81
Substandard | Originated Loans and Leases | Commercial leases
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	6	6
Substandard | Originated Loans and Leases | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	1	1
Substandard | Loans Acquired in a Business Combination | Total commercial loans and leases
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	152	234
Substandard | Loans Acquired in a Business Combination | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	127	191
Substandard | Loans Acquired in a Business Combination | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	25	43
Doubtful | Originated Loans and Leases | Total commercial loans and leases
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	3	0
Doubtful | Originated Loans and Leases | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	1	0
Doubtful | Originated Loans and Leases | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	2	0
Doubtful | Originated Loans and Leases | Commercial leases
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	0	0
Doubtful | Originated Loans and Leases | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	0	0
Doubtful | Loans Acquired in a Business Combination | Total commercial loans and leases
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	0	0
Doubtful | Loans Acquired in a Business Combination | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	0	0
Doubtful | Loans Acquired in a Business Combination | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	$ 0	$ 0