Activity in the ALLL by segment (Detail) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2018		Sep. 30, 2017		Sep. 30, 2018		Sep. 30, 2017		Jun. 30, 2018		Dec. 31, 2017		Jun. 30, 2017		Dec. 31, 2016
Allowance for Loan and Lease Losses [Roll Forward]
Provision for loan losses	$ 61		$ 119		$ 128		$ 324
Allowance for Loan and Lease Losses, Write-offs	(122)		(109)		(329)		(357)
Loan recoveries	34		31		89		96
Loans and Leases Receivable, Allowance	1,623		1,772		1,623		1,772		$ 1,650		$ 1,735		$ 1,731		$ 1,709
Unfunded commitments reserve	72	[1]	73	[2]	72	[1]	73	[2]	72	[1]	79	[1]	72	[2]	67	[2]
Provision for Other Credit Losses	0	[1]	1	[2]	(7)	[1]	6	[2]
Financing Receivable, Allowance for Credit Losses	1,695		1,845		1,695		1,845
Commercial Portfolio Segment [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Provision for loan losses	36		5		37		89
Allowance for Loan and Lease Losses, Write-offs	(51)		(33)		(95)		(122)
Loan recoveries	9		11		19		32
Loans and Leases Receivable, Allowance	1,062		1,123		1,062		1,123		1,068		1,101		1,140		1,124
Unfunded commitments reserve	72	[1]	73	[2]	72	[1]	73	[2]	72	[1]	79	[1]	72	[2]	67	[2]
Provision for Other Credit Losses	0	[1]	1	[2]	(7)	[1]	6	[2]
Financing Receivable, Allowance for Credit Losses	1,134		1,196		1,134		1,196
Consumer Portfolio Segment [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Provision for loan losses	25		114		91		235
Allowance for Loan and Lease Losses, Write-offs	(71)		(76)		(234)		(235)
Loan recoveries	25		20		70		64
Loans and Leases Receivable, Allowance	561		649		561		649		$ 582		$ 634		$ 591		$ 585
Financing Receivable, Allowance for Credit Losses	$ 561		$ 649		$ 561		$ 649

[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.