Securities - Available for Sale Securities (Unrealized Loss Position) (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Fair value, less than 12 months	$ 1,464	$ 31	$ 3
Gross unrealized losses, less than 12 months	5
Fair value, 12 months or longer	3	3
Gross unrealized losses, 12 months or longer
Fair Value	1,467	34	3
Gross unrealized losses, Total	5
Collateralized mortgage obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value, less than 12 months	1,443		2
Gross unrealized losses, less than 12 months	5
Gross unrealized losses, 12 months or longer
Fair Value	1,443		2
Gross unrealized losses, Total	5
Other mortgage-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value, less than 12 months	1
Gross unrealized losses, 12 months or longer
Fair Value	1
Other securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value, less than 12 months	20	31
Fair value, 12 months or longer	3	3
Gross unrealized losses, 12 months or longer
Fair Value	23	34
State and political subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value, less than 12 months			1
Gross unrealized losses, 12 months or longer
Fair Value			$ 1