Investment Securities - Investment Securities Held-to-Maturity (Detail) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities, Amortized Cost	$ 43,393	$ 42,991
Held-to-maturity securities, Unrealized Gains	98	106
Held-to-maturity securities, Unrealized Losses Other	(585)	(662)
Held-to-maturity securities, Fair Value	42,906	42,435
U.S. Treasury and Agencies [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities, Amortized Cost	5,576	5,246
Held-to-maturity securities, Unrealized Gains	14	12
Held-to-maturity securities, Unrealized Losses Other	(113)	(132)
Held-to-maturity securities, Fair Value	5,477	5,126
Mortgage-Backed Securities Residential [Member] | Agency [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities, Amortized Cost	37,774	37,706
Held-to-maturity securities, Unrealized Gains	75	85
Held-to-maturity securities, Unrealized Losses Other	(472)	(529)
Held-to-maturity securities, Fair Value	37,377	37,262
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, Fair Value	1	1
Asset-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities, Amortized Cost	8
Held-to-maturity securities, Fair Value	16
Asset-Backed Securities [Member] | Collateralized Loan Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities, Unrealized Gains	6	5
Held-to-maturity securities, Fair Value	6	5
Asset-Backed Securities [Member] | Asset-Backed Securities Other [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities, Amortized Cost	8	8
Held-to-maturity securities, Unrealized Gains	2	3
Held-to-maturity securities, Fair Value	10	11
Obligations of State and Political Subdivisions [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities, Amortized Cost	6	6
Held-to-maturity securities, Unrealized Gains	1	1
Held-to-maturity securities, Fair Value	7	7
Obligations of Foreign Governments [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities, Amortized Cost	13	9
Held-to-maturity securities, Fair Value	13	9
Other Debt Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities, Amortized Cost	15	15
Held-to-maturity securities, Unrealized Losses Other		(1)
Held-to-maturity securities, Fair Value	$ 15	$ 14