Activity in the ALLL by segment (Detail) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015	Dec. 31, 2014
Allowance for Loan and Lease Losses [Roll Forward]
Provision for loan losses	$ 103	$ 55
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
Commercial Portfolio Segment [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Provision for loan losses	98	7
Allowance for Loan and Lease Losses, Write-offs	(32)	(28)
Loan recoveries	10	11
Loans and Leases Receivable, Allowance	1,123	976	1,047	986
Residential Portfolio Segment [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Provision for loan losses	(32)	25
Allowance for Loan and Lease Losses, Write-offs	(41)	(68)
Loan recoveries	6	9
Loans and Leases Receivable, Allowance	467	743	534	777
Consumer Portfolio Segment [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Provision for loan losses	37	23
Allowance for Loan and Lease Losses, Write-offs	(39)	(34)
Loan recoveries	11	11
Loans and Leases Receivable, Allowance	$ 180	$ 174	$ 171	$ 174

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

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- Definition

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.

+ References

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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
-Paragraph 11B
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=49124121&loc=SL6953423-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=49124121&loc=SL6953423-111524

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.7(d))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (b)(1)(ii)
-URI http://asc.fasb.org/extlink&oid=6379141&loc=d3e15032-111544

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Staff Accounting Bulletin (SAB)
-Number Topic 6
-Section L
-Subsection 1

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- Definition

Amount of expense related to estimated loss from loan and lease transactions.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.11)
-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
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-Section 45
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-URI http://asc.fasb.org/extlink&oid=49124121&loc=SL6953423-111524

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