Securities Available for Sale (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013		Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 23,243		$ 21,087
Unrealized Gains	534		880
Unrealized Losses	388		14
Available-for-sale Securities	23,389		21,953
US Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	793		212
Unrealized Gains	7		10
Unrealized Losses	22		0
Available-for-sale Securities	778		222
US Government Agencies Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,203		1,987
Unrealized Gains	57		85
Unrealized Losses	38		3
Available-for-sale Securities	2,222		2,069
US States and Political Subdivisions Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	248		310
Unrealized Gains	10		15
Unrealized Losses	2		5
Available-for-sale Securities	256		320
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	18,784		17,416
Unrealized Gains	453		756
Unrealized Losses	324		3
Available-for-sale Securities	18,913		18,169
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	181		205
Unrealized Gains	1		4
Unrealized Losses	1		0
Available-for-sale Securities	181		209
Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	124		214
Unrealized Gains	2		5
Unrealized Losses	1		3
Available-for-sale Securities	125		216
Other Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	37		42
Unrealized Gains	3		4
Unrealized Losses	0		0
Available-for-sale Securities	40		46
Equity Securities, Other [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	873	[1]	701	[1]
Unrealized Gains	1	[1]	1	[1]
Unrealized Losses	0	[1]	0	[1]
Available-for-sale Securities	$ 874	[1]	$ 702	[1]

[1] At June 30, 2013, other equity securities was comprised of the following: $334 million in FHLB of Atlanta stock, $402 million in Federal Reserve Bank stock, $137 million in mutual fund investments, and $1 million of other. At December 31, 2012, other equity securities was comprised of the following: $229 million in FHLB of Atlanta stock, $402 million in Federal Reserve Bank stock, $69 million in mutual fund investments, and $2 million of other.