Credit Quality (Summary of the ALLL and Related Loans and Leases Classified by Portfolio Segment) (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated for impairment	$ 170	$ 141
Collectively evaluated for impairment	911	852
Unallocated	121	110
Total allowance for loan and lease losses	1,202	1,103	$ 1,196	$ 1,253
Individually evaluated for impairment	1,529	1,291
Collectively evaluated for impairment	107,295	93,795
Purchased credit impaired	551
Total portfolio loans and leases	109,375	95,086
Commercial Portfolio Segment [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated for impairment	82	42
Collectively evaluated for impairment	628	603
Unallocated	0	0
Total allowance for loan and lease losses	710	645	753	831
Individually evaluated for impairment	413	277
Collectively evaluated for impairment	69,047	59,294
Purchased credit impaired	498
Total portfolio loans and leases	69,958	59,571
Residential Mortgage Loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated for impairment	55	61
Collectively evaluated for impairment	18	20
Unallocated	0	0
Total allowance for loan and lease losses	73	81	89	96
Individually evaluated for impairment	814	736
Collectively evaluated for impairment	15,690	14,589
Purchased credit impaired	37
Total portfolio loans and leases	16,541	15,325
Consumer Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated for impairment	33	38
Collectively evaluated for impairment	265	229
Unallocated	0	0
Total allowance for loan and lease losses	298	267	234	214
Individually evaluated for impairment	302	278
Collectively evaluated for impairment	22,558	19,912
Purchased credit impaired	16
Total portfolio loans and leases	22,876	20,190
Unallocated
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	0	0
Unallocated	121	110
Total allowance for loan and lease losses	121	110	$ 120	$ 112
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	0	0
Purchased credit impaired	0
Total portfolio loans and leases	$ 0	$ 0

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Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

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