Activity in the Allowance for Credit Losses (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015	Dec. 31, 2014
Components:
Allowance for credit losses		$ 1,831	$ 1,947	$ 1,815	$ 1,991
Provision for loan losses		103	55
Provision for Other Credit Losses		(2)	0
Allowance for Loan and Lease Losses, Write-offs		(112)	(130)
Loan recoveries		27	31
Loans and Leases Receivable, Allowance		1,770	1,893	$ 1,752	$ 1,937
Unfunded commitments reserve	[1]	$ 61	$ 54

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