Asset Quality - Changes in Liability for Credit Losses on Lending Related Commitments (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Receivables [Abstract]
Balance at beginning of period	$ 37	$ 29	$ 45
Provision (credit) for losses on lending-related commitments	(2)us-gaap_ProvisionForOtherCreditLosses	8us-gaap_ProvisionForOtherCreditLosses	(16)us-gaap_ProvisionForOtherCreditLosses
Balance at end of period	$ 36	$ 37	$ 29

Amount of expense related to credit loss from transactions other than loan and lease transactions.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph 11

-Article 9

Name:	us-gaap_ProvisionForOtherCreditLosses
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration