Securities - Amortized Cost and Fair Value of Securities Available-for-Sale and Held-to-Maturity (Parenthetical) (Detail) (USD $)	Sep. 30, 2012 Security	Dec. 31, 2011 Security
Schedule of Available-for-sale Securities [Line Items]
Securities at amortized cost of issued or guaranteed	$ 60,666,000,000	$ 51,791,000,000
Securities at amortized cost issued or guaranteed, held to maturity	2,000,000,000	2,300,000,000
Foreign bonds issued by the governments of Greece, Ireland, Italy, Portugal or Spain	0	0
Foreign debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities at amortized cost of issued or guaranteed	5,488,000,000	6,640,000,000
Equity securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities at amortized cost of issued or guaranteed	167,000,000	130,000,000
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	15,289,000,000	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	155,000,000	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 at amortized cost issued or guaranteed, held to maturity	532,000,000	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 at amortized cost issued or guaranteed, held to maturity	680,000,000	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	16,000,000	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