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.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-SubTopic 210
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Name:	us-gaap_LoansAndLeasesReceivableAllowance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Loans and Leases - Additional Allowance for Credit Losses Relating to Loans Acquired In Business Combination (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and leases receivable, allowance	$ 196	$ 180	$ 175	$ 158
Loans Acquired in a Business Combination
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and leases receivable, allowance	7	7	$ 7	$ 7
Loans Acquired in a Business Combination \| Total commercial loans and leases
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and leases receivable, allowance	4	6
Loans Acquired in a Business Combination \| Commercial real estate
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and leases receivable, allowance	4	2
Loans Acquired in a Business Combination \| Commercial and industrial
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and leases receivable, allowance	0	4
Loans Acquired in a Business Combination \| Total consumer loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and leases receivable, allowance	3	1
Loans Acquired in a Business Combination \| Direct installment
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and leases receivable, allowance	$ 1	$ 1