Securities Available for Sale (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 23,072		$ 21,087
Unrealized Gains	799		880
Unrealized Losses	48		14
Available-for-sale Securities	23,823		21,953
US Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	805		212
Unrealized Gains	15		10
Unrealized Losses	0		0
Available-for-sale Securities	820		222
US Government Agencies Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,211		1,987
Unrealized Gains	79		85
Unrealized Losses	5		3
Available-for-sale Securities	2,285		2,069
US States and Political Subdivisions Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	280		310
Unrealized Gains	12		15
Unrealized Losses	2		5
Available-for-sale Securities	290		320
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	18,618		17,416
Unrealized Gains	677		756
Unrealized Losses	40		3
Available-for-sale Securities	19,255		18,169
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	195		205
Unrealized Gains	7		4
Unrealized Losses	0		0
Available-for-sale Securities	202		209
Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	153		214
Unrealized Gains	4		5
Unrealized Losses	1		3
Available-for-sale Securities	156		216
Corporate And Other Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	41		42
Unrealized Gains	4		4
Unrealized Losses	0		0
Available-for-sale Securities	45		46
Equity Securities, Other [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	769	[1]	701	[1]
Unrealized Gains	1	[1]	1	[1]
Unrealized Losses	0	[1]	0	[1]
Available-for-sale Securities	$ 770	[1]	$ 702	[1]

[1] At March 31, 2013, other equity securities was comprised of the following: $268 million in FHLB of Atlanta stock, $402 million in Federal Reserve Bank stock, $98 million in mutual fund investments, and $2 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.