Gross Unrealized Losses and Fair Value of the Company's Investments Securities with Unrealized Losses (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012
Schedule of Available-for-sale Securities [Line Items]
Fair Value Less Than 12 Months	$ 1,564
Unrealized Losses Less Than 12 Months	(3)
Fair Value 12 Months or Greater	126
Unrealized Losses 12 Months or Greater	(25)
Fair Value Total	1,690
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Losses, Total	(28)
Fair Value Less Than 12 Months	3,132
Unrealized Losses Less Than 12 Months	(6)
Fair Value 12 Months or Greater	1,862
Unrealized Losses 12 Months or Greater	(223)
Fair Value Total	4,994
Unrealized Losses Total	(229)
Asset Backed Securities Other
Schedule of Available-for-sale Securities [Line Items]
Fair Value Less Than 12 Months	1
Fair Value 12 Months or Greater	11
Unrealized Losses 12 Months or Greater	(6)
Fair Value Total	12
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Losses, Total	(6)
Fair Value 12 Months or Greater	2
Unrealized Losses 12 Months or Greater	(1)
Fair Value Total	2
Unrealized Losses Total	(1)
Obligations of state and political subdivisions
Schedule of Available-for-sale Securities [Line Items]
Fair Value 12 Months or Greater	5
Fair Value Total	5
Fair Value Less Than 12 Months	89
Fair Value 12 Months or Greater	4
Fair Value Total	93
Other Investments
Schedule of Available-for-sale Securities [Line Items]
Fair Value 12 Months or Greater	99
Unrealized Losses 12 Months or Greater	(19)
Fair Value Total	99
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Losses, Total	(19)
U.S. Treasury and Agencies
Schedule of Available-for-sale Securities [Line Items]
Fair Value Less Than 12 Months	10
Fair Value Total	10
Obligations of Foreign Governments
Schedule of Available-for-sale Securities [Line Items]
Fair Value Less Than 12 Months	6
Fair Value Total	6
Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Fair Value 12 Months or Greater	624
Unrealized Losses 12 Months or Greater	(106)
Fair Value Total	624
Unrealized Losses Total	(106)
Perpetual preferred securities
Schedule of Available-for-sale Securities [Line Items]
Fair Value Less Than 12 Months	22
Fair Value 12 Months or Greater	140
Unrealized Losses 12 Months or Greater	(19)
Fair Value Total	162
Unrealized Losses Total	(19)
Other Investment Securities
Schedule of Available-for-sale Securities [Line Items]
Fair Value 12 Months or Greater	3
Fair Value Total	3
Residential Agency | Residential
Schedule of Available-for-sale Securities [Line Items]
Fair Value Less Than 12 Months	1,563
Unrealized Losses Less Than 12 Months	(3)
Fair Value 12 Months or Greater	7
Fair Value Total	1,570
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Losses, Total	(3)
Fair Value Less Than 12 Months	3,005
Unrealized Losses Less Than 12 Months	(6)
Fair Value 12 Months or Greater	153
Fair Value Total	3,158
Unrealized Losses Total	(6)
Residential non-agency non-prime | Residential
Schedule of Available-for-sale Securities [Line Items]
Fair Value 12 Months or Greater	1	[1]
Fair Value Total	1	[1]
Fair Value 12 Months or Greater	311	[2]
Unrealized Losses 12 Months or Greater	(49)	[2]
Fair Value Total	311	[2]
Unrealized Losses Total	(49)	[2]
Non-agency | Commercial Mortgage-Backed Securities
Schedule of Available-for-sale Securities [Line Items]
Fair Value 12 Months or Greater	3
Fair Value Total	3
Residential non-agency prime | Residential
Schedule of Available-for-sale Securities [Line Items]
Fair Value 12 Months or Greater	625	[3]
Unrealized Losses 12 Months or Greater	(48)	[3]
Fair Value Total	625	[3]
Unrealized Losses Total	$ (48)	[3]

[1] The Company has $97 million of unrealized losses on residential non-agency mortgage-backed securities. Credit-related other-than-temporary impairment on these securities may occur if there is further deterioration in the underlying collateral pool performance. Borrower defaults may increase if current economic conditions persist or worsen. Additionally, further deterioration in home prices may increase the severity of projected losses.

[2] Includes all securities not meeting the conditions to be designated as prime.

[3] Prime securities are those designated as such by the issuer at origination. When an issuer designation is unavailable, the Company determines at acquisition date the categorization based on asset pool characteristics (such as weighted-average credit score, loan-to-value, loan type, prevalence of low documentation loans) and deal performance (such as pool delinquencies and security market spreads).