Securities - Available for Sale Securities (Unrealized Loss Position) (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Fair value, less than 12 months	$ 31	$ 4
Gross unrealized losses, less than 12 months
Fair value, 12 months or longer	3
Gross unrealized losses, 12 months or longer
Fair Value	34	4
Gross unrealized losses, Total
Collateralized mortgage obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value, less than 12 months		1
Gross unrealized losses, less than 12 months
Gross unrealized losses, 12 months or longer
Fair Value		1
Gross unrealized losses, Total
Other securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value, less than 12 months	31	3
Gross unrealized losses, less than 12 months
Fair value, 12 months or longer	3
Gross unrealized losses, 12 months or longer
Fair Value	34	3
Gross unrealized losses, Total