Securities Available for Sale (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended		12 Months Ended
	Sep. 30, 2014		Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 25,852		$ 22,622
Unrealized Gains	541		454
Unrealized Losses	231		534
Available-for-sale Securities	26,162		22,542
US Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,007		1,334
Unrealized Gains	6		6
Unrealized Losses	2		47
Available-for-sale Securities	1,011		1,293
US Government Agencies Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	986		1,028
Unrealized Gains	15		13
Unrealized Losses	31		57
Available-for-sale Securities	970		984
US States and Political Subdivisions Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	228		232
Unrealized Gains	9		7
Unrealized Losses	0		2
Available-for-sale Securities	237		237
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	22,508		18,915
Unrealized Gains	501		421
Unrealized Losses	198		425
Available-for-sale Securities	22,811		18,911
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	129		155
Unrealized Gains	3		1
Unrealized Losses	0		2
Available-for-sale Securities	132		154
Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	19		78
Unrealized Gains	2		2
Unrealized Losses	0		1
Available-for-sale Securities	21		79
Other Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	38		39
Unrealized Gains	3		3
Unrealized Losses	0		0
Available-for-sale Securities	41		42
Equity Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	937	[1]	841	[1]
Unrealized Gains	2	[1]	1	[1]
Unrealized Losses	0		0
Available-for-sale Securities	$ 939	[1]	$ 842	[1]

[1] At September 30, 2014, other equity securities comprised the following: $421 million in FHLB of Atlanta stock, $402 million in Federal Reserve Bank stock, $109 million in mutual fund investments, and $7 million of other. At December 31, 2013, other equity securities comprised 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.