LOANS AND LEASES - Commercial Loans and Leases by Credit Quality (Detail) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Financing Receivable, Credit Quality Indicator [Line Items]
Total commercial loans and leases	$ 23,070	$ 22,153
Commercial Real Estate [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total commercial loans and leases	8,916	8,786
Commercial and Industrial [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total commercial loans and leases	5,205	4,556
Commercial Leases [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total commercial loans and leases	417	373
Other [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total commercial loans and leases	35	46
Total Commercial Loans and Leases [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total commercial loans and leases	14,573	13,761
Originated Loans and Leases [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total commercial loans and leases	19,872	18,062
Originated Loans and Leases [Member] | Commercial Real Estate [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total commercial loans and leases	6,864	6,171
Originated Loans and Leases [Member] | Commercial and Industrial [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total commercial loans and leases	4,925	4,140
Originated Loans and Leases [Member] | Commercial Leases [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total commercial loans and leases	417	373
Originated Loans and Leases [Member] | Other [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total commercial loans and leases	35	46
Originated Loans and Leases [Member] | Total Commercial Loans and Leases [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total commercial loans and leases	12,241	10,730
Acquired Loans [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total commercial loans and leases	3,198	4,091
Acquired Loans [Member] | Commercial Real Estate [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total commercial loans and leases	2,052	2,615
Acquired Loans [Member] | Commercial and Industrial [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total commercial loans and leases	280	416
Acquired Loans [Member] | Total Commercial Loans and Leases [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total commercial loans and leases	2,332	3,031
Pass [Member] | Originated Loans and Leases [Member] | Commercial Real Estate [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total commercial loans and leases	6,570	5,883
Pass [Member] | Originated Loans and Leases [Member] | Commercial and Industrial [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total commercial loans and leases	4,587	3,879
Pass [Member] | Originated Loans and Leases [Member] | Commercial Leases [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total commercial loans and leases	408	366
Pass [Member] | Originated Loans and Leases [Member] | Other [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total commercial loans and leases	34	45
Pass [Member] | Originated Loans and Leases [Member] | Total Commercial Loans and Leases [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total commercial loans and leases	11,599	10,173
Pass [Member] | Acquired Loans [Member] | Commercial Real Estate [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total commercial loans and leases	1,772	2,256
Pass [Member] | Acquired Loans [Member] | Commercial and Industrial [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total commercial loans and leases	241	355
Pass [Member] | Acquired Loans [Member] | Total Commercial Loans and Leases [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total commercial loans and leases	2,013	2,611
Special Mention [Member] | Originated Loans and Leases [Member] | Commercial Real Estate [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total commercial loans and leases	150	163
Special Mention [Member] | Originated Loans and Leases [Member] | Commercial and Industrial [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total commercial loans and leases	195	180
Special Mention [Member] | Originated Loans and Leases [Member] | Commercial Leases [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total commercial loans and leases	6	1
Special Mention [Member] | Originated Loans and Leases [Member] | Other [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total commercial loans and leases	0	0
Special Mention [Member] | Originated Loans and Leases [Member] | Total Commercial Loans and Leases [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total commercial loans and leases	351	344
Special Mention [Member] | Acquired Loans [Member] | Commercial Real Estate [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total commercial loans and leases	117	168
Special Mention [Member] | Acquired Loans [Member] | Commercial and Industrial [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total commercial loans and leases	14	18
Special Mention [Member] | Acquired Loans [Member] | Total Commercial Loans and Leases [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total commercial loans and leases	131	186
Substandard [Member] | Originated Loans and Leases [Member] | Commercial Real Estate [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total commercial loans and leases	143	125
Substandard [Member] | Originated Loans and Leases [Member] | Commercial and Industrial [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total commercial loans and leases	138	81
Substandard [Member] | Originated Loans and Leases [Member] | Commercial Leases [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total commercial loans and leases	3	6
Substandard [Member] | Originated Loans and Leases [Member] | Other [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total commercial loans and leases	1	1
Substandard [Member] | Originated Loans and Leases [Member] | Total Commercial Loans and Leases [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total commercial loans and leases	285	213
Substandard [Member] | Acquired Loans [Member] | Commercial Real Estate [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total commercial loans and leases	163	191
Substandard [Member] | Acquired Loans [Member] | Commercial and Industrial [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total commercial loans and leases	25	43
Substandard [Member] | Acquired Loans [Member] | Total Commercial Loans and Leases [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total commercial loans and leases	188	234
Doubtful [Member] | Originated Loans and Leases [Member] | Commercial Real Estate [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total commercial loans and leases	1	0
Doubtful [Member] | Originated Loans and Leases [Member] | Commercial and Industrial [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total commercial loans and leases	5	0
Doubtful [Member] | Originated Loans and Leases [Member] | Commercial Leases [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total commercial loans and leases	0	0
Doubtful [Member] | Originated Loans and Leases [Member] | Other [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total commercial loans and leases	0	0
Doubtful [Member] | Originated Loans and Leases [Member] | Total Commercial Loans and Leases [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total commercial loans and leases	6	0
Doubtful [Member] | Acquired Loans [Member] | Commercial Real Estate [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total commercial loans and leases	0	0
Doubtful [Member] | Acquired Loans [Member] | Commercial and Industrial [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total commercial loans and leases	0	0
Doubtful [Member] | Acquired Loans [Member] | Total Commercial Loans and Leases [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total commercial loans and leases	$ 0	$ 0