Investment Securities - Investment Securities Available for Sale (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	$ 55,981		$ 55,432
Available-for-sale securities, Unrealized Gains	1,063		980
Available-for-sale securities, Unrealized Losses Other-than-Temporary	(3)		(3)
Available-for-sale securities, Unrealized Losses Other	(215)		(340)
Available-for-sale securities, Fair Value	56,826	[1]	56,069	[1]
U.S. Treasury and Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	2,560		2,622
Available-for-sale securities, Unrealized Gains	32		14
Available-for-sale securities, Unrealized Losses Other-than-Temporary	0
Available-for-sale securities, Unrealized Losses Other	0		(4)
Available-for-sale securities, Fair Value	2,592		2,632
Mortgage-Backed Securities Residential [Member] | Agency [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	45,506		44,668
Available-for-sale securities, Unrealized Gains	658		593
Available-for-sale securities, Unrealized Losses Other-than-Temporary	0
Available-for-sale securities, Unrealized Losses Other	(134)		(244)
Available-for-sale securities, Fair Value	46,030		45,017
Mortgage-Backed Securities Residential [Member] | Non-Agency Prime [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	380		399
Available-for-sale securities, Unrealized Gains	9		9
Available-for-sale securities, Unrealized Losses Other-than-Temporary	(2)		(2)
Available-for-sale securities, Unrealized Losses Other	(2)		(1)
Available-for-sale securities, Fair Value	385		405
Mortgage-Backed Securities Residential [Member] | Non-Agency Non-Prime [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	254		261
Available-for-sale securities, Unrealized Gains	20		20
Available-for-sale securities, Unrealized Losses Other-than-Temporary	(1)		(1)
Available-for-sale securities, Unrealized Losses Other	0
Available-for-sale securities, Fair Value	273		280
Commercial [Member] | Agency [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	101		112
Available-for-sale securities, Unrealized Gains	2		3
Available-for-sale securities, Unrealized Losses Other-than-Temporary	0
Available-for-sale securities, Unrealized Losses Other	0
Available-for-sale securities, Fair Value	103		115
Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	621
Available-for-sale securities, Fair Value	638
Asset-Backed Securities [Member] | Collateralized Loan Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	18		18
Available-for-sale securities, Unrealized Gains	4		4
Available-for-sale securities, Unrealized Losses Other-than-Temporary	0
Available-for-sale securities, Unrealized Losses Other	0
Available-for-sale securities, Fair Value	22		22
Asset-Backed Securities [Member] | Asset-Backed Securities Other [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	603		607
Available-for-sale securities, Unrealized Gains	13		13
Available-for-sale securities, Unrealized Losses Other-than-Temporary	0
Available-for-sale securities, Unrealized Losses Other	0		(1)
Available-for-sale securities, Fair Value	616		619
Obligations of State and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	5,477		5,604
Available-for-sale securities, Unrealized Gains	260		265
Available-for-sale securities, Unrealized Losses Other-than-Temporary	0
Available-for-sale securities, Unrealized Losses Other	(2)		(1)
Available-for-sale securities, Fair Value	5,735		5,868
Obligations of Foreign Governments [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	0		6
Available-for-sale securities, Unrealized Gains	0
Available-for-sale securities, Unrealized Losses Other-than-Temporary	0
Available-for-sale securities, Unrealized Losses Other	0
Available-for-sale securities, Fair Value	0		6
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	690		690
Available-for-sale securities, Unrealized Gains	6		3
Available-for-sale securities, Unrealized Losses Other-than-Temporary	0
Available-for-sale securities, Unrealized Losses Other	(68)		(79)
Available-for-sale securities, Fair Value	628		614
Perpetual Preferred Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	156		200
Available-for-sale securities, Unrealized Gains	29		27
Available-for-sale securities, Unrealized Losses Other-than-Temporary	0
Available-for-sale securities, Unrealized Losses Other	(9)		(10)
Available-for-sale securities, Fair Value	176		217
Other Investment [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	236		245
Available-for-sale securities, Unrealized Gains	30		29
Available-for-sale securities, Unrealized Losses Other-than-Temporary	0
Available-for-sale securities, Unrealized Losses Other	0
Available-for-sale securities, Fair Value	$ 266		$ 274

[1] Includes only collateral pledged by the Company where counterparties have the right to sell or pledge the collateral.