Activity in the Allowance for Credit Losses (Detail) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015
Components:
Allowance for credit losses		$ 1,845	$ 1,811	$ 1,845	$ 1,811	$ 1,803	$ 1,776	$ 1,840	$ 1,815
Provision for loan losses		119	95	324	338
Provision for Other Credit Losses		1	2	6	5
Allowance for Loan and Lease Losses, Write-offs		(109)	(150)	(357)	(428)
Loan recoveries		31	24	96	81
Loans and Leases Receivable, Allowance		1,772	1,743	1,772	1,743	$ 1,731	$ 1,709	$ 1,774	$ 1,752
Unfunded commitments reserve	[1]	$ 73	$ 68	$ 73	$ 68

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