Activity in the Allowance for Credit Losses (Detail) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2019		Sep. 30, 2018		Sep. 30, 2019		Sep. 30, 2018		Jun. 30, 2019		Dec. 31, 2018		Jun. 30, 2018		Dec. 31, 2017
Components:
Allowance for credit losses	$ 1,771		$ 1,695		$ 1,771		$ 1,695
Provision for loan losses	130		61		409		128
Provision for Other Credit Losses	2	[1]	0	[2]	3	[1]	(7)	[2]
Allowance for Loan and Lease Losses, Write-offs	(139)		(122)		(377)		(329)
Loan recoveries	27		34		83		89
Allowance for Loan and Lease Losses, Adjustments, Other	0				(31)	[3]
Loans and Leases Receivable, Allowance	1,699		1,623		1,699		1,623		$ 1,681		$ 1,615		$ 1,650		$ 1,735
Unfunded commitments reserve	72	[1]	72	[2]	72	[1]	72	[2]	70	[1]	69	[1]	72	[2]	79	[2]
Commercial Portfolio Segment [Member]
Components:
Allowance for credit losses	1,286		1,134		1,286		1,134
Provision for loan losses	42		36		208		37
Provision for Other Credit Losses	2	[1]	0	[2]	3	[1]	(7)	[2]
Allowance for Loan and Lease Losses, Write-offs	(35)		(51)		(88)		(95)
Loan recoveries	5		9		14		19
Allowance for Loan and Lease Losses, Adjustments, Other	0				0
Loans and Leases Receivable, Allowance	1,214		1,062		1,214		1,062		1,202		1,080		1,068		1,101
Unfunded commitments reserve	72	[1]	72	[2]	72	[1]	72	[2]	70	[1]	69	[1]	72	[2]	79	[2]
Consumer Portfolio Segment [Member]
Components:
Allowance for credit losses	485		561		485		561
Provision for loan losses	88		25		201		91
Allowance for Loan and Lease Losses, Write-offs	(104)		(71)		(289)		(234)
Loan recoveries	22		25		69		70
Allowance for Loan and Lease Losses, Adjustments, Other	0				(31)	[3]
Loans and Leases Receivable, Allowance	$ 485		$ 561		$ 485		$ 561		$ 479		$ 535		$ 582		$ 634

[1] The unfunded commitments reserve is recorded in Other liabilities in the Consolidated Balance Sheets.

[2] The unfunded commitments reserve is recorded in Other liabilities in the Consolidated Balance Sheets

[3] Represents the allowance for restructured loans that were transferred from LHFI to LHFS in the first quarter of 2019 and subsequently sold in the second quarter of 2019.