Securities Available for Sale (Addition Information) (Detail) - USD ($) $ in Millions		3 Months Ended			6 Months Ended
		Jun. 30, 2016		Jun. 30, 2015	Jun. 30, 2016		Jun. 30, 2015	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Gross Realized Gains		$ 4		$ 14	$ 4		$ 14
Available-for-sale Securities		29,336			29,336			$ 27,825
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities	[1]	694			694			533
Federal Home Loan Bank (FHLB) of Atlanta stock (par value)		202			202			32
Federal Reserve Bank Stock		402			402			402
Mutual fund investments (par value)		84			84			93
Fair Value, Inputs, Level 3 [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities	[2]	713			713			556
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities		713			713			556
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		610	[3]		610	[3]		440	[4]
Investments, Fair Value Disclosure		$ 6			$ 6			$ 6

[1] At June 30, 2016, the fair value of other equity securities was comprised of the following: $202 million of FHLB of Atlanta stock, $402 million of Federal Reserve Bank of Atlanta stock, $84 million of mutual fund investments, and $6 million of other.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.

[2] Trading assets and derivative instruments, securities AFS, and trading liabilities and derivative instruments that are classified as level 1 are valued based on quoted market prices. For those instruments classified as level 2 or 3, refer to the respective valuation discussions within this footnote.

[3] Includes $84 million of mutual fund investments, $202 million of FHLB of Atlanta stock, $402 million of Federal Reserve Bank of Atlanta stock, and $6 million of other.

[4] 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.