Activity in the ALLL by segment (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
Allowance for Loan and Lease Losses [Roll Forward]
Provision for loan losses	$ 130		$ 61		$ 409		$ 128
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)	[1]
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	[2]	72	[3]	72	[2]	72	[3]	70	[2]	69	[2]	72	[3]	79	[3]
Provision for Other Credit Losses	2	[2]	0	[3]	3	[2]	(7)	[3]
Financing Receivable, Allowance for Credit Loss	1,771		1,695		1,771		1,695
Commercial Portfolio Segment [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Provision for loan losses	42		36		208		37
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	[2]	72	[3]	72	[2]	72	[3]	70	[2]	69	[2]	72	[3]	79	[3]
Provision for Other Credit Losses	2	[2]	0	[3]	3	[2]	(7)	[3]
Financing Receivable, Allowance for Credit Loss	1,286		1,134		1,286		1,134
Consumer Portfolio Segment [Member]
Allowance for Loan and Lease Losses [Roll Forward]
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)	[1]
Loans and Leases Receivable, Allowance	485		561		485		561		$ 479		$ 535		$ 582		$ 634
Financing Receivable, Allowance for Credit Loss	$ 485		$ 561		$ 485		$ 561

[1] 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.

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

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