Rollforward of Credit Losses Recognized in Earnings Related to Securities (Detail) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
		Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016
Debt Securities, Available-for-sale [Line Items]
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Period Increase (Decrease)			$ 0	$ 1		$ 0
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Reductions, Securities Sold			(23)
Available-for-sale Securities	[1],[2]	$ 31,442	31,442	30,947	[3]
Ending balance		0	0	$ 23		$ 23
Gains on sale of OTTI securities		$ 6	$ 6

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

[2] Includes securities AFS pledged as collateral where counterparties have the right to sell or repledge the collateral of $222 million and $223 million at December?31, 2018 and December?31, 2017, respectively.

[3] Beginning January 1, 2018, the Company reclassified equity securities previously presented in Securities AFS to Other assets on the Consolidated Balance Sheets. Prior periods have been revised to conform to the current presentation for comparability. See Note 11, "Other Assets," for additional information.