Gross Realized Gains and Losses on Sales and OTTI on Securities Available for Sale (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
Available-for-sale Securities	[1]	$ 27,113		$ 27,113		$ 26,770
Gross realized gains		14	$ 0	14	$ 0
Available-for-sale Securities, Gross Realized Losses		0	0	0	(1)
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities		0	(1)	0	(1)
Gain (Loss) on Sale of Securities, Net		(14)	1	(14)	2
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Available-for-sale Securities		112		112		$ 123
Mortgage-backed Securities, Issued by Private Enterprises [Member] | Other Than Temporarily Impaired Securities [Member]
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.