Securities Available for Sale (Addition Information) (Detail) - USD ($) $ in Millions		Mar. 31, 2018		Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities	[1],[2]	$ 30,934		$ 30,947	[3]
Federal Home Loan Bank (FHLB) of Atlanta stock (par value)	[4]	15		15
Federal Reserve Bank Stock	[4]	403		403
Mutual Fund Investments	[4]	135		49
Fair Value, Inputs, Level 3 [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities		0		72
Fair Value, Measurements, Recurring [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities		30,934	[5]	30,947	[6]
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities		$ 0	[5]	$ 72	[6]

[1] Includes securities AFS pledged as collateral where counterparties have the right to sell or repledge the collateral of $214 million and $223 million at March 31, 2018 and December 31, 2017, respectively.

[2] Text selection found with no content.

[3] Beginning January 1, 2018, the Company reclassified equity securities previously presented in Securities available for sale to Other assets on the Consolidated Balance Sheets. Reclassifications have been made to previously reported amounts for comparability. See Note 9, "Other Assets," for additional information.

[4] Beginning January 1, 2018, the Company reclassified equity securities previously presented in Securities available for sale to Other assets on the Consolidated Balance Sheets. Reclassifications have been made to previously reported amounts for comparability.

[5] Beginning January 1, 2018, the Company reclassified equity securities previously presented in Securities available for sale to Other assets on the Consolidated Balance Sheets. Reclassifications have been made to previously reported amounts for comparability. See Note 9, "Other Assets," for additional information.

[6] Beginning January 1, 2018, the Company reclassified equity securities previously presented in Securities available for sale to Other assets on the Consolidated Balance Sheets. Reclassifications have been made to previously reported amounts for comparability. See Note 9, "Other Assets," for additional information.