Fair Value and Gross Unrealized Losses on Available-for-Sale Securities (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	$ 7,849	$ 2,239
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	(156)	(21)
12 months or more Fair Value	137
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	3
Total Fair Value	7,986	2,239
Total Unrealized Losses	(159)	(21)
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	7,221	1,784
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	(150)	(18)
12 months or more Fair Value	1
Total Fair Value	7,222	1,784
Total Unrealized Losses	(150)	(18)
Other Debt Securities
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	595	454
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	(5)	(3)
12 months or more Fair Value	132
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	3
Total Fair Value	727	454
Total Unrealized Losses	(8)	(3)
Other Debt And Equity Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	33	1
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	1
12 months or more Fair Value	4
Total Fair Value	37	1
Total Unrealized Losses	$ 1