Securities - Amortized Cost and Fair Value of Securities Available-for-Sale and Held-to-Maturity (Parenthetical) (Detail) (USD $)	Dec. 31, 2012		Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Securities at amortized cost of issued or guaranteed	$ 66,041,000,000		$ 51,791,000,000
Securities held-to-maturity, fair value	1,800,000,000		2,300,000,000
Foreign debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities at amortized cost of issued or guaranteed	5,385,000,000	[1],[2]	6,640,000,000	[1],[2]
Equity securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities at amortized cost of issued or guaranteed	167,000,000	[3]	130,000,000	[3]
Mortgage-backed securities, U.S. Government agency issued or guaranteed [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities at amortized cost of issued or guaranteed	15,646,000,000		15,357,000,000
Federal National Mortgage Association Certificates and Obligations (FNMA) [Member] | US Government Agency Issued or Guaranteed [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities at amortized cost of issued or guaranteed	153,000,000		27,000,000
Federal National Mortgage Association Certificates and Obligations (FNMA) [Member] | Equity securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Preferred equity securities at amortized cost			2,000,000
Preferred equity securities reflect cumulative other-than-temporary impairment charges			173,000,000
Federal National Mortgage Association Certificates and Obligations (FNMA) [Member] | Mortgage-backed securities, U.S. Government agency issued or guaranteed [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities held-to-maturity, fair value	507,000,000		591,000,000
Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC) [Member] | US Government Agency Issued or Guaranteed [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities at amortized cost of issued or guaranteed	13,000,000		13,000,000
Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC) [Member] | Mortgage-backed securities, U.S. Government agency issued or guaranteed [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities held-to-maturity, fair value	614,000,000		830,000,000
FDIC [Member] | Corporate and other domestic [Member]
Schedule of Available-for-sale Securities [Line Items]
Other domestic debt securities at amortized cost			516,000,000
Foreign Government [Member] | Foreign debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Foreign debt securities fully backed by foreign governments	$ 1,500,000,000		$ 2,700,000,000

[1] We did not hold any foreign debt securities issued by the governments of Greece, Ireland, Italy, Portugal or Spain at December 31, 2012 and 2011.

[2] At December 31, 2012 and 2011, foreign debt securities consisted of $1.5 billion and $2.7 billion, respectively, of securities fully backed by foreign governments. The remainder of foreign debt securities represents foreign bank or corporate debt.

[3] Includes preferred equity securities at amortized cost issued by FNMA of $2 million at December 31, 2011 which reflects cumulative other-than-temporary impairment charges of $173 million.