Securities - Securities by Maturity (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013
Investments Debt And Equity Securities [Abstract]
Amortized Cost of Securities Available for sale, Due in one year or less	$ 492
Amortized Cost of Securities Available for sale, Due after one through five years	10,938
Amortized Cost of Securities Available for sale, Due after five through ten years	1,169
Amortized Cost of Securities Available for sale, Due after ten years	4
Total Amortized Cost of Securities Available for sale	12,603
Fair Value of Securities Available for sale, Due in one year or less	500
Fair Value of Securities Available for sale, Due after one through five years	10,982
Fair Value of Securities Available for sale, Due after five through ten years	1,119
Fair Value of Securities Available for sale, Due after ten years	5
Total Fair Value of Securities Available for sale	12,606
Amortized Cost of Held-to-Maturity Securities, Due in one year or less	7
Amortized Cost of Held-to-Maturity Securities, Due after one through five years	4,682
Amortized Cost of Held-to-Maturity Securities, Due after five through ten years	146
Amortized Cost of Held-to-Maturity Securities, Due after ten years
Total Amortized Cost of Held-to-Maturity securities	4,835
Fair Value of Held-to-Maturity Securities, Due in one year or less	6
Fair Value of Held-to-Maturity Securities, Due after one through five years	4,584
Fair Value of Held-to-Maturity Securities, Due after five through ten years	140
Fair Value of Held-to-Maturity Securities, Due after ten years
Total Fair Value of Held-to-Maturity Securities	$ 4,730

Amount of available-for-sale debt securities at cost, net of adjustments, maturing in the sixth fiscal year through the tenth fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings (less any cumulative-effect adjustments, as defined) and fair value hedge accounting adjustments.

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 210.5-02.2)

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

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

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS115-1/124-1

-Paragraph 7

-Footnote 2

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 20

-Subparagraph c

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.