Securities Available for Sale (Detail) - USD ($) $ in Millions		6 Months Ended	12 Months Ended
		Jun. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		$ 26,779	$ 26,257
Unrealized Gains		503	600
Unrealized Losses		169	87
Available-for-sale Securities	[1]	27,113	26,770
US Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		2,905	1,913
Unrealized Gains		16	9
Unrealized Losses		8	1
Available-for-sale Securities		2,913	1,921
US Government Agencies Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		466	471
Unrealized Gains		13	15
Unrealized Losses		2	2
Available-for-sale Securities		477	484
US States and Political Subdivisions Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		178	200
Unrealized Gains		6	9
Unrealized Losses		0	0
Available-for-sale Securities		184	209
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		22,431	22,573
Unrealized Gains		461	558
Unrealized Losses		159	83
Available-for-sale Securities		22,733	23,048
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		110	122
Unrealized Gains		2	2
Unrealized Losses		0	1
Available-for-sale Securities		112	123
Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		15	19
Unrealized Gains		2	2
Unrealized Losses		0	0
Available-for-sale Securities		17	21
Other Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		35	38
Unrealized Gains		2	3
Unrealized Losses		0	0
Available-for-sale Securities		37	41
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	[2]	639	921
Unrealized Gains	[2]	1	2
Unrealized Losses		0	0
Available-for-sale Securities	[2]	$ 640	$ 923

[1] Includes securities AFS pledged as collateral where counterparties have the right to sell or repledge the collateral of $0 million and $369 million at June 30, 2015 and December 31, 2014, respectively.

[2] At June 30, 2015, the fair value of other equity securities was comprised of the following: $174 million in FHLB of Atlanta stock, $402 million in Federal Reserve Bank of Atlanta stock, $58 million in mutual fund investments, and $6 million of other. At December 31, 2014, the fair value of other equity securities was comprised of the following: $376 million in FHLB of Atlanta stock, $402 million in Federal Reserve Bank of Atlanta stock, $138 million in mutual fund investments, and $7 million of other.