Securities - Available for Sale Securities (Unrealized Loss Position) (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012
Schedule of Available-for-sale Securities [Line Items]
Fair value, less than 12 months	$ 8,565	$ 31	$ 213
Gross unrealized losses, less than 12 months	166		1
Fair value, 12 months or longer		3
Gross unrealized losses, 12 months or longer
Fair Value	8,565	34	213
Gross unrealized losses, Total	166		1
Gross unrealized losses	1	1	1
Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value, less than 12 months	5,412		1
Gross unrealized losses, less than 12 months	113
Gross unrealized losses, 12 months or longer
Fair Value	5,412		1
Gross unrealized losses, Total	113
Held-to-maturity Securities, Collateralized mortgage obligations Fair Value less than 12 months	2,998		200
Held-to-maturity Securities, Gross unrealized losses, less than 12 months	50
Held-to-maturity Securities, Collateralized mortgage obligations Fair Value 12 months or longer
Held-to-maturity Securities, Gross unrealized losses, 12 months or longer
Held-to-maturity Securities, Collateralized mortgage obligations Fair Value	2,998		200
Held-to-maturity Securities, Gross unrealized losses	50
State and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses, 12 months or longer
Other Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value, less than 12 months	152
Gross unrealized losses, less than 12 months	3
Gross unrealized losses, 12 months or longer
Fair Value	152
Gross unrealized losses, Total	3
Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value, less than 12 months	3	31	12
Gross unrealized losses, less than 12 months			1
Fair value, 12 months or longer		3
Gross unrealized losses, 12 months or longer
Fair Value	3	34	12
Gross unrealized losses, Total			$ 1