Asset Quality - Credit Risk Profile by Regulatory Classifications (Detail) (Residential - Prime, Financing Receivable [Member], USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Financing Receivable, Recorded Investment [Line Items]
Total	$ 12,764	$ 12,368
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	12,445	12,029
Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	$ 319	$ 339

Net amount of the investment in a contractual right to receive money on demand or on fixed or determinable dates that is recognized as an asset in the creditor's statement of financial position. Examples include, but are not limited to, credit card receivables, notes receivable and receivables relating to lessor's rights to payments from leases other than operating leases that have been recorded as assets. Excludes trade accounts receivable with contractual maturity of one year or less and arose from the sale of goods or services.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.3)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 3

-Article 5

Name:	us-gaap_NotesReceivableNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant