Securities Available for Sale (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		$ 27,568	$ 26,257
Unrealized Gains		424	600
Unrealized Losses		167	87
Available-for-sale Securities	[1]	27,825	26,770
US Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		3,460	1,913
Unrealized Gains		3	9
Unrealized Losses		14	1
Available-for-sale Securities		3,449	1,921
US Government Agencies Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		402	471
Unrealized Gains		10	15
Unrealized Losses		1	2
Available-for-sale Securities		411	484
US States and Political Subdivisions Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		156	200
Unrealized Gains		8	9
Unrealized Losses		0	0
Available-for-sale Securities		164	209
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		22,877	22,573
Unrealized Gains		397	558
Unrealized Losses		150	83
Available-for-sale Securities		23,124	23,048
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		92	122
Unrealized Gains		2	2
Unrealized Losses		0	1
Available-for-sale Securities		94	123
Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		11	19
Unrealized Gains		2	2
Unrealized Losses		1	0
Available-for-sale Securities		12	21
Other Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		37	38
Unrealized Gains		1	3
Unrealized Losses		0	0
Available-for-sale Securities		38	41
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	[2]	533	921
Unrealized Gains	[2]	1	2
Unrealized Losses	[2]	1	0
Available-for-sale Securities	[2]	$ 533	$ 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 December 31, 2015 and December 31, 2014, respectively.

[2] At December 31, 2015, the fair value of other equity securities was comprised of the following: $32 million of FHLB of Atlanta stock, $402 million of Federal Reserve Bank of Atlanta stock, $93 million of 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 of FHLB of Atlanta stock, $402 million of Federal Reserve Bank of Atlanta stock, $138 million of mutual fund investments, and $7 million of other.