Gross Realized Gains and Losses on Sales and OTTI on Securities Available for Sale (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013		Dec. 31, 2013
Available-for-sale Securities	$ 26,162				$ 26,162				$ 22,542
Gross realized gains	3		0		3		4
Available-for-sale Securities, Gross Realized Losses	(12)		0		(13)		(1)
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities	0		0		(1)		(1)
Gain (Loss) on Sale of Securities, Net	(9)	[1]	0	[1]	(11)	[1]	2	[1]
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Available-for-sale Securities	132				132				154
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities	0		0		(1)		(1)
Mortgage-backed Securities, Issued by Private Enterprises [Member] | Other Than Temporarily Impaired Securities [Member]
Available-for-sale Securities	$ 19		$ 23		$ 19		$ 23

[1] Total OTTI was $0 for the three and nine months ended September 30, 2014 and 2013. There were no OTTI gains/losses recognized in earnings or recognized as non-credit related OTTI in OCI for both the three months ended September 30, 2014 and 2013. Of total OTTI, losses of $1 million were recognized in earnings, and gains of $1 million were recognized as non-credit-related OTTI in OCI for both the nine months ended September 30, 2014 and 2013.