Investment Securities - Schedule of Gross Unrealized Losses and Fair Value of Company's Investment Securities with Unrealized Losses (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014
Schedule Of Fair Value And Gross Unrealized Losses [Abstract]
Fair Value Less Than 12 Months	$ 23,462
Unrealized Losses Less Than 12 Months	(491)
Fair Value 12 Months or Greater	1,224
Unrealized Losses 12 Months or Greater	(57)
Fair Value Total	24,686
Unrealized Losses Total	(548)
Fair Value Less Than 12 Months	16,011
Unrealized Losses Less Than 12 Months	(382)
Fair Value 12 Months or Greater	3,540
Unrealized Losses 12 Months or Greater	(214)
Fair Value Total	19,551
Unrealized Losses Total	(596)
U.S. Treasury and agencies [Member]
Schedule Of Fair Value And Gross Unrealized Losses [Abstract]
Fair Value Less Than 12 Months	1,012
Unrealized Losses Less Than 12 Months	(59)
Fair Value 12 Months or Greater
Unrealized Losses 12 Months or Greater
Fair Value Total	1,012
Unrealized Losses Total	(59)
Fair Value Less Than 12 Months	845
Unrealized Losses Less Than 12 Months	(41)
Fair Value 12 Months or Greater	95
Unrealized Losses 12 Months or Greater	(5)
Fair Value Total	940
Unrealized Losses Total	(46)
Mortgage-backed securities Residential [Member] | Agency [Member]
Schedule Of Fair Value And Gross Unrealized Losses [Abstract]
Fair Value Less Than 12 Months	22,447
Unrealized Losses Less Than 12 Months	(432)
Fair Value 12 Months or Greater	1,202
Unrealized Losses 12 Months or Greater	(44)
Fair Value Total	23,649
Unrealized Losses Total	(476)
Fair Value Less Than 12 Months	14,566
Unrealized Losses Less Than 12 Months	(323)
Fair Value 12 Months or Greater	2,580
Unrealized Losses 12 Months or Greater	(117)
Fair Value Total	17,146
Unrealized Losses Total	(440)
Mortgage-backed securities Residential [Member] | Non-agency Prime [Member]
Schedule Of Fair Value And Gross Unrealized Losses [Abstract]
Fair Value Less Than 12 Months	47
Unrealized Losses Less Than 12 Months	(1)
Fair Value 12 Months or Greater	175
Unrealized Losses 12 Months or Greater	(7)
Fair Value Total	222
Unrealized Losses Total	(8)
Mortgage-backed securities Residential [Member] | Non-agency Non-prime [Member]
Schedule Of Fair Value And Gross Unrealized Losses [Abstract]
Fair Value Less Than 12 Months	33
Unrealized Losses Less Than 12 Months
Fair Value 12 Months or Greater	44
Unrealized Losses 12 Months or Greater	(3)
Fair Value Total	77
Unrealized Losses Total	(3)
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	23
Unrealized Losses Less Than 12 Months
Fair Value 12 Months or Greater	3
Unrealized Losses 12 Months or Greater
Fair Value Total	26
Unrealized Losses Total
Obligations of state and political subdivisions [Member]
Schedule Of Fair Value And Gross Unrealized Losses [Abstract]
Fair Value Less Than 12 Months	3
Unrealized Losses Less Than 12 Months
Fair Value 12 Months or Greater
Unrealized Losses 12 Months or Greater
Fair Value Total	3
Unrealized Losses Total
Fair Value Less Than 12 Months	441
Unrealized Losses Less Than 12 Months	(17)
Fair Value 12 Months or Greater	81
Unrealized Losses 12 Months or Greater	(4)
Fair Value Total	522
Unrealized Losses Total	(21)
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	12
Unrealized Losses 12 Months or Greater	(11)
Fair Value Total	12
Unrealized Losses Total	(11)
Obligations of foreign governments [Member]
Schedule Of Fair Value And Gross Unrealized Losses [Abstract]
Fair Value Less Than 12 Months	6
Unrealized Losses Less Than 12 Months
Fair Value 12 Months or Greater
Unrealized Losses 12 Months or Greater
Fair Value Total	6
Unrealized Losses Total
Corporate debt securities [Member]
Schedule Of Fair Value And Gross Unrealized Losses [Abstract]
Fair Value Less Than 12 Months	50
Unrealized Losses Less Than 12 Months
Fair Value 12 Months or Greater	442
Unrealized Losses 12 Months or Greater	(65)
Fair Value Total	492
Unrealized Losses Total	(65)
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	120
Unrealized Losses 12 Months or Greater	(13)
Fair Value Total	120
Unrealized Losses Total	$ (13)