Rollforward of Credit Losses Recognized in Earnings Related to Securities (Detail) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities		$ 0	$ 1	$ 0	$ 1
Available-for-sale Securities	[1]	27,113		27,113		$ 26,770
Ending balance		25	25	25	25
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities		112		112		$ 123
Mortgage-backed Securities, Issued by Private Enterprises [Member] | Other Than Temporarily Impaired Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities		$ 0	$ 19	$ 0	$ 19

[1] Includes securities AFS pledged as collateral where counterparties have the right to sell or repledge the collateral of $0 million and $369 million at June 30, 2015 and December 31, 2014, respectively.