Credit Quality (Summary of the ALLL and Related Loans and Leases Classified by Portfolio Segment) (Detail) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated	$ 255	$ 170
Collectively evaluated	2,093	911
Unallocated		121
Total allowance for loan and lease losses	2,348	1,202	$ 1,115	$ 1,103
Individually evaluated	1,656	1,529
Collectively evaluated	115,688	107,295
Purchased credit impaired	508	551
Total portfolio loans and leases	117,852	109,375
Commercial Portfolio Segment [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated	118	82
Collectively evaluated	1,195	628
Unallocated		0
Total allowance for loan and lease losses	1,313	710	654	645
Individually evaluated	547	413
Collectively evaluated	76,989	69,047
Purchased credit impaired	459	498
Total portfolio loans and leases	77,995	69,958
Residential Mortgage Loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated	77	55
Collectively evaluated	183	18
Unallocated		0
Total allowance for loan and lease losses	260	73	79	81
Individually evaluated	813	814
Collectively evaluated	15,674	15,690
Purchased credit impaired	29	37
Total portfolio loans and leases	16,516	16,541
Consumer Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated	60	33
Collectively evaluated	715	265
Unallocated		0
Total allowance for loan and lease losses	775	298	270	267
Individually evaluated	296	302
Collectively evaluated	23,025	22,558
Purchased credit impaired	20	16
Total portfolio loans and leases	23,341	22,876
Unallocated
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated		0
Collectively evaluated		0
Unallocated		121
Total allowance for loan and lease losses	$ 0	121	$ 112	$ 110
Individually evaluated		0
Collectively evaluated		0
Purchased credit impaired		0
Total portfolio loans and leases		$ 0

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The balance of financing receivables that were acquired with deteriorated credit quality.

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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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