Securities Available for Sale (Addition Information) (Detail) - USD ($) $ in Millions		Dec. 31, 2017		Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities	[1]	$ 31,416		$ 30,672
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities	[2]	469		642
Federal Home Loan Bank (FHLB) of Atlanta stock (par value)		15		132
Federal Reserve Bank Stock		403		402
Mutual fund investments (par value)		49		102
Fair Value, Inputs, Level 3 [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities	[3]	490		633
Fair Value, Measurements, Recurring [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities		31,416		30,672
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities		490		633
Equity Securities [Member] | Fair Value, Measurements, Recurring [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Fair Value Disclosure		2		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		$ 418	[4]	$ 540	[5]

[1] Includes securities AFS pledged as collateral where counterparties have the right to sell or repledge the collateral of $223 million and $0 million at December 31, 2017 and December 31, 2016, respectively.

[2] At December 31, 2017, the fair value of other equity securities was comprised of the following: $15 million of FHLB of Atlanta stock, $403 million of Federal Reserve Bank of Atlanta stock, $49 million of mutual fund investments, and $2 million of other.At December 31, 2016, the fair value of other equity securities was comprised of the following: $132 million of FHLB of Atlanta stock, $402 million of Federal Reserve Bank of Atlanta stock, $102 million of mutual fund investments, and $6 million of other.

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

[4] Includes $49 million of mutual fund investments, $15 million of FHLB of Atlanta stock, $403 million of Federal Reserve Bank of Atlanta stock, and $2 million of other.

[5] Includes $102 million of mutual fund investments, $132 million of FHLB of Atlanta stock, $402 million of Federal Reserve Bank of Atlanta stock, and $6 million of other.