Securities Available for Sale (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2014		Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 23,211		$ 22,622
Unrealized Gains	484		454
Unrealized Losses	393		534
Available-for-sale Securities	23,302		22,542
US Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,582		1,334
Unrealized Gains	7		6
Unrealized Losses	32		47
Available-for-sale Securities	1,557		1,293
US Government Agencies Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,015		1,028
Unrealized Gains	15		13
Unrealized Losses	43		57
Available-for-sale Securities	987		984
US States and Political Subdivisions Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	281		232
Unrealized Gains	6		7
Unrealized Losses	0		2
Available-for-sale Securities	287		237
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	19,317		18,915
Unrealized Gains	447		421
Unrealized Losses	317		425
Available-for-sale Securities	19,447		18,911
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	147		155
Unrealized Gains	2		1
Unrealized Losses	0		2
Available-for-sale Securities	149		154
Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	65		78
Unrealized Gains	3		2
Unrealized Losses	1		1
Available-for-sale Securities	67		79
Other Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	39		39
Unrealized Gains	3		3
Unrealized Losses	0		0
Available-for-sale Securities	42		42
Equity Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	765	[1]	841	[1]
Unrealized Gains	1	[1]	1	[1]
Unrealized Losses	0		0
Available-for-sale Securities	$ 766	[1]	$ 842	[1]

[1] At March 31, 2014, other equity securities was comprised of the following: $308 million in FHLB of Atlanta stock, $402 million in Federal Reserve Bank stock, $54 million in mutual fund investments, and $2 million of other. At December 31, 2013, other equity securities was comprised of the following: $336 million in FHLB of Atlanta stock, $402 million in Federal Reserve Bank stock, $103 million in mutual fund investments, and $1 million of other.