Securities - Details of Securities (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 12,412	$ 12,446	$ 13,166
Gross Unrealized Gains	165	183	335
Gross Unrealized Losses	218	283	5
Fair Value	12,359	12,346	13,496
Held to maturities, Amortized Cost	4,826	4,756	3,721
Held to maturities, Gross Unrealized Gains	9	6	58
Held to maturities, Gross Unrealized Losses	102	145
Held to maturities, Fair Value	4,733	4,617	3,779
States and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	37	39	47
Gross Unrealized Gains		1	1
Gross Unrealized Losses
Fair Value	37	40	48
Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	10,541	11,120	12,633
Gross Unrealized Gains	136	152	290
Gross Unrealized Losses	208	272	5
Fair Value	10,469	11,000	12,918
Held to maturities, Amortized Cost	4,806	4,736	3,703
Held to maturities, Gross Unrealized Gains	9	6	58
Held to maturities, Gross Unrealized Losses	102	145
Held to maturities, Fair Value	4,713	4,597	3,761
Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	17	17	41
Gross Unrealized Gains	4	3	2
Gross Unrealized Losses
Fair Value	21	20	43
Held to maturities, Amortized Cost	20	20	18
Held to maturities, Gross Unrealized Gains
Held to maturities, Gross Unrealized Losses
Held to maturities, Fair Value	20	20	18
Other Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,817	1,270	445
Gross Unrealized Gains	25	27	42
Gross Unrealized Losses	10	11
Fair Value	$ 1,832	$ 1,286	$ 487