Investment Securities - Gross Unrealized Losses and Fair Value of Company's Investments Securities with Unrealized Losses (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013
Schedule Of Fair Value And Gross Unrealized Losses [Abstract]
Fair Value Less Than 12 Months	$ 21,099
Unrealized Losses Less Than 12 Months	(512)
Fair Value 12 Months or Greater	108
Unrealized Losses 12 Months or Greater	(16)
Fair Value Total	21,207
Unrealized Losses Total	(528)
Fair Value Less Than 12 Months	16,340
Unrealized Losses Less Than 12 Months	(496)
Fair Value 12 Months or Greater	1,175
Unrealized Losses 12 Months or Greater	(128)
Fair Value Total	17,515
Unrealized Losses Total	(624)
U.S. Treasury and agencies [Member]
Schedule Of Fair Value And Gross Unrealized Losses [Abstract]
Fair Value Less Than 12 Months	1,056
Unrealized Losses Less Than 12 Months	(60)
Fair Value 12 Months or Greater
Unrealized Losses 12 Months or Greater
Fair Value Total	1,056
Unrealized Losses Total	(60)
Fair Value Less Than 12 Months	853
Unrealized Losses Less Than 12 Months	(51)
Fair Value 12 Months or Greater
Unrealized Losses 12 Months or Greater
Fair Value Total	853
Unrealized Losses Total	(51)
Residential [Member] | Agency [Member]
Schedule Of Fair Value And Gross Unrealized Losses [Abstract]
Fair Value Less Than 12 Months	20,034
Unrealized Losses Less Than 12 Months	(452)
Fair Value 12 Months or Greater	85
Unrealized Losses 12 Months or Greater	(2)
Fair Value Total	20,119
Unrealized Losses Total	(454)
Fair Value Less Than 12 Months	13,540
Unrealized Losses Less Than 12 Months	(389)
Fair Value 12 Months or Greater	343
Unrealized Losses 12 Months or Greater	(3)
Fair Value Total	13,883
Unrealized Losses Total	(392)
Residential [Member] | Residential Non-Agency Prime [Member]
Schedule Of Fair Value And Gross Unrealized Losses [Abstract]
Fair Value Less Than 12 Months	137
Unrealized Losses Less Than 12 Months	(2)
Fair Value 12 Months or Greater	206
Unrealized Losses 12 Months or Greater	(13)
Fair Value Total	343
Unrealized Losses Total	(15)
Residential [Member] | Residential Non-Agency Non-Prime [Member]
Schedule Of Fair Value And Gross Unrealized Losses [Abstract]
Fair Value Less Than 12 Months	128
Unrealized Losses Less Than 12 Months	(2)
Fair Value 12 Months or Greater	81
Unrealized Losses 12 Months or Greater	(5)
Fair Value Total	209
Unrealized Losses Total	(7)
Commercial [Member] | Agency [Member]
Schedule Of Fair Value And Gross Unrealized Losses [Abstract]
Fair Value Less Than 12 Months	61
Unrealized Losses Less Than 12 Months
Fair Value 12 Months or Greater
Unrealized Losses 12 Months or Greater
Fair Value Total	61
Unrealized Losses Total
Commercial [Member] | Non-Agency [Member]
Schedule Of Fair Value And Gross Unrealized Losses [Abstract]
Fair Value Less Than 12 Months	1
Unrealized Losses Less Than 12 Months
Fair Value 12 Months or Greater
Unrealized Losses 12 Months or Greater
Fair Value Total	1
Unrealized Losses Total
Asset Backed Securities Other [Member]
Schedule Of Fair Value And Gross Unrealized Losses [Abstract]
Fair Value Less Than 12 Months
Unrealized Losses Less Than 12 Months
Fair Value 12 Months or Greater	10
Unrealized Losses 12 Months or Greater	(2)
Fair Value Total	10
Unrealized Losses Total	(2)
Fair Value Less Than 12 Months	25
Unrealized Losses Less Than 12 Months	(1)
Fair Value 12 Months or Greater	3
Unrealized Losses 12 Months or Greater
Fair Value Total	28
Unrealized Losses Total	(1)
Obligations of state and political subdivisions [Member]
Schedule Of Fair Value And Gross Unrealized Losses [Abstract]
Fair Value Less Than 12 Months	8
Unrealized Losses Less Than 12 Months
Fair Value 12 Months or Greater
Unrealized Losses 12 Months or Greater
Fair Value Total	8
Unrealized Losses Total
Fair Value Less Than 12 Months	1,382
Unrealized Losses Less Than 12 Months	(46)
Fair Value 12 Months or Greater	10
Unrealized Losses 12 Months or Greater
Fair Value Total	1,392
Unrealized Losses Total	(46)
Other debt securities [Member]
Schedule Of Fair Value And Gross Unrealized Losses [Abstract]
Fair Value Less Than 12 Months
Unrealized Losses Less Than 12 Months
Fair Value 12 Months or Greater	13
Unrealized Losses 12 Months or Greater	(12)
Fair Value Total	13
Unrealized Losses Total	(12)
Corporate debt securities [Member]
Schedule Of Fair Value And Gross Unrealized Losses [Abstract]
Fair Value Less Than 12 Months	214
Unrealized Losses Less Than 12 Months	(5)
Fair Value 12 Months or Greater	420
Unrealized Losses 12 Months or Greater	(87)
Fair Value Total	634
Unrealized Losses Total	(92)
Perpetual preferred securities [Member]
Schedule Of Fair Value And Gross Unrealized Losses [Abstract]
Fair Value Less Than 12 Months
Unrealized Losses Less Than 12 Months
Fair Value 12 Months or Greater	112
Unrealized Losses 12 Months or Greater	(20)
Fair Value Total	112
Unrealized Losses Total	$ (20)