Securities Available for Sale - Additional Information (Detail) (USD $) Share data in Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2013	Dec. 31, 2013 Mortgage-backed Securities, Issued by Private Enterprises [Member]	Dec. 31, 2012 Mortgage-backed Securities, Issued by Private Enterprises [Member]	Dec. 31, 2013 Other Than Temporarily Impaired Securities [Member] Mortgage-backed Securities, Issued by Private Enterprises [Member]	Dec. 31, 2012 Other Than Temporarily Impaired Securities [Member] Mortgage-backed Securities, Issued by Private Enterprises [Member]	Dec. 31, 2011 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 Pledged as Collateral	$ 10,600,000,000	$ 11,000,000,000
Securities AFS Pledged Transferee Can Transfer	0	0
Sold equity forward agreement underlying shares	59
Executed equity forward agreement underlying shares	60
Contributed equity forward agreement underlying shares	1
Net gain on sale of certain other equity securities	1,900,000,000
Noncash Contribution Expense	38,000,000
Available-for-sale Securities	$ 21,953,000,000	$ 22,542,000,000	$ 154,000,000	$ 209,000,000	$ 22,000,000	$ 209,000,000	$ 167,000,000