Derivatives (Risk Ratings of the Notional Amount of Risk Participation Agreements) (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Derivatives, Fair Value
Notional amount of the risk participations agreements	$ 2,467	$ 1,664
Pass
Derivatives, Fair Value
Notional amount of the risk participations agreements	2,447	1,650
Risk Level, Special Mention
Derivatives, Fair Value
Notional amount of the risk participations agreements	14	7
Risk Level, Substandard
Derivatives, Fair Value
Notional amount of the risk participations agreements	$ 6	$ 7

Nominal or face amount used to calculate payments on the derivative liability.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=64837297&loc=SL5580258-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Notional Amount
-URI http://asc.fasb.org/extlink&oid=6519104

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=64837297&loc=SL5579245-113959

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant