Securities - Amortized Cost and Fair Value of Asset Backed Securities (Detail) - USD ($) $ in Millions		Jun. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities		$ 33,002	$ 29,654
Unrealized Gains, Available-for-sale securities		458	621
Unrealized Losses, Available-for-sale securities		(375)	(135)
Fair Value, Available-for-sale securities		33,085	30,140
Amortized Cost, Held-to-Maturity Securities		14,160	13,469
Unrealized Gains, Held-to-maturity securities		199	229
Unrealized Losses, Held-to-maturity securities		(32)	(3)
Held-to-maturity Securities, Fair Value		14,327	13,695
U.S. Treasury [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities		10,738	11,793
Unrealized Gains, Available-for-sale securities		207	276
Unrealized Losses, Available-for-sale securities		(125)	(58)
Fair Value, Available-for-sale securities		10,820	12,011
Mortgage-backed securities [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities	[1]	699	520
Unrealized Gains, Available-for-sale securities	[1]	0	5
Unrealized Losses, Available-for-sale securities	[1]	(13)	(1)
Fair Value, Available-for-sale securities	[1]	686	524
Amortized Cost, Held-to-Maturity Securities	[2]	5,059	4,868
Unrealized Gains, Held-to-maturity securities	[2]	115	120
Unrealized Losses, Held-to-maturity securities	[2]	(10)	(1)
Held-to-maturity Securities, Fair Value	[2]	5,164	4,987
Collateralized mortgage obligations [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities	[1]	160	35
Unrealized Gains, Available-for-sale securities	[1]	0	0
Unrealized Losses, Available-for-sale securities	[1]	0	0
Fair Value, Available-for-sale securities	[1]	160	35
Direct agency obligations [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities	[1]	4,039	3,995
Unrealized Gains, Available-for-sale securities	[1]	178	217
Unrealized Losses, Available-for-sale securities	[1]	(6)	(6)
Fair Value, Available-for-sale securities	[1]	4,211	4,206
Mortgage-backed securities, issued or guaranteed by US Government agency [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities		11,893	7,985
Unrealized Gains, Available-for-sale securities		53	101
Unrealized Losses, Available-for-sale securities		(177)	(27)
Fair Value, Available-for-sale securities		11,769	8,059
Amortized Cost, Held-to-Maturity Securities		3,565	3,700
Unrealized Gains, Held-to-maturity securities		11	53
Unrealized Losses, Held-to-maturity securities		(14)	(1)
Held-to-maturity Securities, Fair Value		3,562	3,752
Collateralized mortgage obligations, issued or guaranteed by US Government agency [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities		564	329
Unrealized Gains, Available-for-sale securities		6	3
Unrealized Losses, Available-for-sale securities		(2)	(2)
Fair Value, Available-for-sale securities		568	330
Amortized Cost, Held-to-Maturity Securities		5,507	4,867
Unrealized Gains, Held-to-maturity securities		71	54
Unrealized Losses, Held-to-maturity securities		(8)	(1)
Held-to-maturity Securities, Fair Value		5,570	4,920
Obligations of U.S. states and political subdivision [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities		818	661
Unrealized Gains, Available-for-sale securities		6	10
Unrealized Losses, Available-for-sale securities		(12)	(4)
Fair Value, Available-for-sale securities		812	667
Amortized Cost, Held-to-Maturity Securities		20	23
Unrealized Gains, Held-to-maturity securities		1	1
Unrealized Losses, Held-to-maturity securities		0	0
Held-to-maturity Securities, Fair Value		21	24
Residential Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Held-to-Maturity Securities		9	11
Unrealized Gains, Held-to-maturity securities		1	1
Unrealized Losses, Held-to-maturity securities		0	0
Held-to-maturity Securities, Fair Value		10	12
Commercial Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities		27	43
Unrealized Gains, Available-for-sale securities		0	0
Unrealized Losses, Available-for-sale securities		0	0
Fair Value, Available-for-sale securities		27	43
Home Equity Backed Securities [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities		91	97
Unrealized Gains, Available-for-sale securities		0	0
Unrealized Losses, Available-for-sale securities		(8)	(8)
Fair Value, Available-for-sale securities		83	89
Other securities [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities		108	110
Unrealized Gains, Available-for-sale securities		0	0
Unrealized Losses, Available-for-sale securities		(14)	(16)
Fair Value, Available-for-sale securities		94	94
Foreign debt securities [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities	[3]	3,703	3,921
Unrealized Gains, Available-for-sale securities	[3]	5	6
Unrealized Losses, Available-for-sale securities	[3]	(16)	(12)
Fair Value, Available-for-sale securities	[3]	3,692	3,915
Foreign debt securities [Member] | Foreign Government [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities		692	689
Equity securities [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities		162	165
Unrealized Gains, Available-for-sale securities		3	3
Unrealized Losses, Available-for-sale securities		(2)	(1)
Fair Value, Available-for-sale securities		163	167
US Government sponsored enterprises [Member] | Federal National Mortgage Association Certificates and Obligations (FNMA) [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities		826	521
Amortized Cost, Held-to-Maturity Securities		3,406	3,185
US Government sponsored enterprises [Member] | Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC) [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities		33	34
Amortized Cost, Held-to-Maturity Securities		$ 1,653	$ 1,683

[1] Includes securities at amortized cost of $826 million and $521 million issued or guaranteed by FNMA at June 30, 2015 and December 31, 2014, respectively, and $33 million and $34 million issued or guaranteed by the Federal Home Loan Mortgage Corporation ("FHLMC") at June 30, 2015 and December 31, 2014, respectively.

[2] Includes securities at amortized cost of $3,406 million and $3,185 million issued or guaranteed by FNMA at June 30, 2015 and December 31, 2014, respectively, and $1,653 million and $1,683 million issued and guaranteed by FHLMC at June 30, 2015 and December 31, 2014, respectively.

[3] At June 30, 2015 and December 31, 2014, foreign debt securities consisted of $692 million and $689 million, respectively, of securities fully backed by foreign governments. The remainder of foreign debt securities represents public sector entity, bank or corporate debt.