Securities Available for Sale (Addition Information) (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Gross Realized Gains		$ 25		$ 28		$ 39
Available-for-sale Securities, Gross Realized Losses		3		42		$ 36
Available-for-sale Securities	[1]	27,825		26,770
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities		94		123
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities	[2]	533		923
Federal Home Loan Bank (FHLB) of Atlanta stock (par value)		32		376
Federal Reserve Bank Stock		402		402
Mutual fund investments (par value)		93		138
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities		556		946
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Fair Value Disclosure		6		7
Other Than Temporarily Impaired Securities [Member] | Mortgage-backed Securities, Issued by Private Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities		20		16
Equity Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities		$ 440	[3]	$ 785	[4]

[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.

[3] Includes $93 million of mutual fund investments, $32 million of FHLB of Atlanta stock, $402 million of Federal Reserve Bank of Atlanta stock, and $6 million of other.

[4] Includes $138 million of mutual fund investments, $376 million of FHLB of Atlanta stock, $402 million of Federal Reserve Bank of Atlanta stock, and $7 million of other.