Securities Available for Sale (Addition Information) (Detail) - USD ($) $ in Millions		3 Months Ended			9 Months Ended
		Sep. 30, 2015		Sep. 30, 2014	Sep. 30, 2015		Sep. 30, 2014	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Gross Realized Gains		$ 11		$ 3	$ 25		$ 3
Available-for-sale Securities, Gross Realized Losses		(3)		12	3		13
Available-for-sale Securities	[1]	27,270			27,270			$ 26,770
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities		102			102			123
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities	[2]	551			551			923
Federal Home Loan Bank (FHLB) of Atlanta stock (par value)		32			32			376
Federal Reserve Bank Stock		402			402			402
Mutual fund investments (par value)		111			111			138
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities		567			567			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			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		22		$ 19	22		$ 19
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]		$ 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 September 30, 2015 and December 31, 2014, respectively.

[2] At September 30, 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, $111 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 $111 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.