Activity in the ALLL by segment (Detail) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2015
Allowance for Loan and Lease Losses [Roll Forward]
Provision for loan losses	$ 117	$ 103
Allowance for Loan and Lease Losses, Write-offs	(146)	(112)
Loan recoveries	34	27
Loans and Leases Receivable, Allowance	1,714	1,770	$ 1,709	$ 1,752
Commercial Portfolio Segment [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Provision for loan losses	46	98
Allowance for Loan and Lease Losses, Write-offs	(63)	(32)
Loan recoveries	13	10
Loans and Leases Receivable, Allowance	1,120	1,123	1,124	1,047
Residential Portfolio Segment [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Provision for loan losses	5	(32)
Allowance for Loan and Lease Losses, Write-offs	(29)	(41)
Loan recoveries	9	6
Loans and Leases Receivable, Allowance	354	467	369	534
Consumer Portfolio Segment [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Provision for loan losses	66	37
Allowance for Loan and Lease Losses, Write-offs	(54)	(39)
Loan recoveries	12	11
Loans and Leases Receivable, Allowance	$ 240	$ 180	$ 216	$ 171

Amount of recovery of loans and lease receivables which had previously been fully or partially written-off as bad debts.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount of loans and leases that have been written off from both loan receivables and allowance reserve for credit loss.

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- Definition

Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
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Amount of expense related to estimated loss from loan and lease transactions.

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-Name Accounting Standards Codification
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