Securities Available for Sale - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2014		Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities Pledged as Collateral		$ 2,600,000,000		$ 11,000,000,000
Available-for-sale Securities		26,770,000,000	[1]	22,542,000,000	[1]
Sold equity forward agreement underlying shares	59,000,000
Executed equity forward agreement underlying shares	60,000,000
Contributed equity forward agreement underlying shares	1,000,000
Net gain on sales of certain other equity securities	1,900,000,000
Noncash Contribution Expense	38,000,000
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities		123,000,000		154,000,000
Other Than Temporarily Impaired Securities [Member] | Mortgage-backed Securities, Issued by Private Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities		$ 16,000,000

[1] Includes loans of consolidated VIEs of $288 million and $327 million at December 31, 2014 and December 31, 2013, respectively.