Rollforward of Credit Losses Recognized in Earnings Related to Securities (Detail) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	[3]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Gross Realized Gains		$ 6	$ 1	$ 7	$ 1
Available-for-sale Securities	[1],[2]	30,942		30,942		$ 30,947
Ending balance		23	22	23	22
Available-for-sale Securities, Gross Realized Losses		6	0	6	0
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Period Increase (Decrease)		0	$ 0	0	$ 0
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 $184 million and $223 million at June 30, 2018 and December 31, 2017, respectively.

[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.