Securities Available for Sale (Addition Information) (Detail) - USD ($) $ in Millions		Mar. 31, 2016		Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities		$ 28,188		$ 27,825
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities	[1]	518		533
Federal Home Loan Bank (FHLB) of Atlanta stock (par value)		64		32
Federal Reserve Bank Stock		402		402
Mutual fund investments (par value)		47		93
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities		580		556
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		5		6
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		$ 471	[2]	$ 440	[3]

[1] At March 31, 2016, the fair value of other equity securities was comprised of the following: $64 million of FHLB of Atlanta stock, $402 million of Federal Reserve Bank of Atlanta stock, $47 million of mutual fund investments, and $5 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] Includes $47 million of mutual fund investments, $64 million of FHLB of Atlanta stock, $402 million of Federal Reserve Bank of Atlanta stock, and $5 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.