Activity in the Allowance for Credit Losses (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Components:
Allowance for credit losses		$ 1,763	$ 1,783	$ 1,814	$ 1,776
Provision for loan losses		38	117
Provision for Other Credit Losses		(10)	2
Allowance for Loan and Lease Losses, Write-offs		(106)	(146)
Loan recoveries		27	34
Loans and Leases Receivable, Allowance		1,694	1,714	$ 1,735	$ 1,709
Unfunded commitments reserve	[1]	$ 69	$ 69

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