Activity in the Allowance for Credit Losses (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
Components:
Allowance for credit losses	$ 1,722		$ 1,803		$ 1,722		$ 1,803
Provision for loan losses	29		87		67		204
Provision for Other Credit Losses	3	[1]	3	[2]	(7)	[1]	5	[2]
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]
Commercial Portfolio Segment [Member]
Components:
Allowance for credit losses	1,140		1,212		1,140		1,212
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
Consumer Portfolio Segment [Member]
Components:
Allowance for credit losses	582		591		582		591
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

[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.