Investment Securities - Investment Securities Held to Maturity (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 19,741	$ 9
Unrealized Losses Recorded in AOCI	(1,465)	0
Securities held to maturity, at carrying value	18,276	9
Gross Unrealized Gains	388	0
Gross Unrealized Losses	(2)	0
Fair value of investment securities held to maturity, Total	18,662	9
Residential Mortgage-Backed Securities Agency [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	18,053
Unrealized Losses Recorded in AOCI	(1,331)
Securities held to maturity, at carrying value	16,722
Gross Unrealized Gains	355
Gross Unrealized Losses	(2)
Fair value of investment securities held to maturity, Total	17,075
Commercial Mortgage-Backed Securities Agency [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	1,688
Unrealized Losses Recorded in AOCI	(134)
Securities held to maturity, at carrying value	1,554
Gross Unrealized Gains	33
Gross Unrealized Losses	0
Fair value of investment securities held to maturity, Total	1,587
Other Asset-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost		9
Unrealized Losses Recorded in AOCI		0
Securities held to maturity, at carrying value		9
Gross Unrealized Gains		0
Gross Unrealized Losses		0
Fair value of investment securities held to maturity, Total		$ 9