Investment Securities - Investment Securities Held-to-Maturity (Detail) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities, Amortized Cost	$ 42,113	$ 43,590
Held-to-maturity securities, Unrealized Gains	469	199
Held-to-maturity securities, Unrealized Losses Other-than-Temporary	0	0
Held-to-maturity securities, Unrealized Losses Other	(61)	(296)
Held-to-maturity securities, Fair Value	42,521	43,493
U.S. Treasury and Agencies [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities, Amortized Cost	2,908	2,925
Held-to-maturity securities, Unrealized Gains	57	14
Held-to-maturity securities, Unrealized Losses Other-than-Temporary	0	0
Held-to-maturity securities, Unrealized Losses Other		(20)
Held-to-maturity securities, Fair Value	2,965	2,919
Mortgage-Backed Securities Residential [Member] | Agency [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities, Amortized Cost	39,160	40,619
Held-to-maturity securities, Unrealized Gains	402	175
Held-to-maturity securities, Unrealized Losses Other-than-Temporary	0	0
Held-to-maturity securities, Unrealized Losses Other	(59)	(273)
Held-to-maturity securities, Fair Value	39,503	40,521
Mortgage-Backed Securities Residential [Member] | Non-Agency Non-Prime [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities, Amortized Cost	1	1
Held-to-maturity securities, Unrealized Losses Other-than-Temporary	0	0
Held-to-maturity securities, Fair Value	1	1
Asset-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities, Amortized Cost	9
Held-to-maturity securities, Fair Value	18
Asset-Backed Securities [Member] | Collateralized Loan Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities, Unrealized Gains	6	6
Held-to-maturity securities, Unrealized Losses Other-than-Temporary	0	0
Held-to-maturity securities, Fair Value	6	6
Asset-Backed Securities [Member] | Asset-Backed Securities Other [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities, Amortized Cost	9	10
Held-to-maturity securities, Unrealized Gains	3	3
Held-to-maturity securities, Unrealized Losses Other-than-Temporary	0	0
Held-to-maturity securities, Fair Value	12	13
Obligations of State and Political Subdivisions [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities, Amortized Cost	8	8
Held-to-maturity securities, Unrealized Gains	1	1
Held-to-maturity securities, Unrealized Losses Other-than-Temporary	0	0
Held-to-maturity securities, Unrealized Losses Other	(1)	(1)
Held-to-maturity securities, Fair Value	8	8
Obligations of Foreign Governments [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities, Amortized Cost	9	9
Held-to-maturity securities, Unrealized Losses Other-than-Temporary	0	0
Held-to-maturity securities, Fair Value	9	9
Other Debt Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities, Amortized Cost	18	18
Held-to-maturity securities, Unrealized Losses Other-than-Temporary	0	0
Held-to-maturity securities, Unrealized Losses Other	(1)	(2)
Held-to-maturity securities, Fair Value	$ 17	$ 16