Activity in the ALLL by segment (Detail) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2018		Jun. 30, 2017		Jun. 30, 2018		Jun. 30, 2017		Mar. 31, 2018		Dec. 31, 2017		Mar. 31, 2017		Dec. 31, 2016
Allowance for Loan and Lease Losses [Roll Forward]
Provision for loan losses	$ 29		$ 87		$ 67		$ 204
Allowance for Loan and Lease Losses, Write-offs	(101)		(101)		(207)		(248)
Loan recoveries	28		31		55		66
Loans and Leases Receivable, Allowance	1,650		1,731		1,650		1,731		$ 1,694		$ 1,735		$ 1,714		$ 1,709
Unfunded commitments reserve	72	[1]	72	[2]	72	[1]	72	[2]	69	[1]	79	[1]	69	[2]	67	[2]
Provision for Other Credit Losses	3	[1]	3	[2]	(7)	[1]	5	[2]
Financing Receivable, Allowance for Credit Losses	1,722		1,803		1,722		1,803
Commercial Portfolio Segment [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Provision for loan losses	17		39		1		84
Allowance for Loan and Lease Losses, Write-offs	(21)		(26)		(44)		(89)
Loan recoveries	4		7		10		21
Loans and Leases Receivable, Allowance	1,068		1,140		1,068		1,140		1,068		1,101		1,120		1,124
Financing Receivable, Allowance for Credit Losses	1,140		1,212		1,140		1,212
Consumer Portfolio Segment [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Provision for loan losses	12		48		66		120
Allowance for Loan and Lease Losses, Write-offs	(80)		(75)		(163)		(159)
Loan recoveries	24		24		45		45
Loans and Leases Receivable, Allowance	582		591		582		591		$ 626		$ 634		$ 594		$ 585
Financing Receivable, Allowance for Credit Losses	$ 582		$ 591		$ 582		$ 591

[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.