Activity in the Allowance for Credit Losses (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
Components:
Allowance for credit losses	$ 1,695		$ 1,845		$ 1,695		$ 1,845
Provision for loan losses	61		119		128		324
Provision for Other Credit Losses	0	[1]	1	[2]	(7)	[1]	6	[2]
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]
Commercial Portfolio Segment [Member]
Components:
Allowance for credit losses	1,134		1,196		1,134		1,196
Provision for loan losses	36		5		37		89
Provision for Other Credit Losses	0	[1]	1	[2]	(7)	[1]	6	[2]
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]
Consumer Portfolio Segment [Member]
Components:
Allowance for credit losses	561		649		561		649
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

[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.