Securities - Details of Securities (Detail) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Available for sale, Amortized Cost	$ 18,253	$ 20,507
Available for sale, Gross Unrealized Gains	35	37
Available for sale, Gross Unrealized Losses	264	332
Available for sale, Fair Value	18,024	20,212
Held to maturities, Amortized Cost	10,638	10,232
Held to maturities, Gross Unrealized Gains	11	2
Held to maturities, Gross Unrealized Losses	186	227
Held to maturities, Fair Value	10,463	10,007
U.S. Treasury, Agencies and Corporations [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for sale, Amortized Cost	170	188
Available for sale, Gross Unrealized Gains	0	0
Available for sale, Gross Unrealized Losses	2	4
Available for sale, Fair Value	168	184
States and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for sale, Amortized Cost	10	11
Available for sale, Gross Unrealized Gains	1	0
Available for sale, Gross Unrealized Losses	0	0
Available for sale, Fair Value	11	11
Agency Residential Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for sale, Amortized Cost	1,646	1,857
Available for sale, Gross Unrealized Gains	4	6
Available for sale, Gross Unrealized Losses	12	17
Available for sale, Fair Value	1,638	1,846
Held to maturities, Amortized Cost	630	629
Held to maturities, Gross Unrealized Gains	1	0
Held to maturities, Gross Unrealized Losses	4	5
Held to maturities, Fair Value	627	624
Agency Commercial Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Held to maturities, Gross Unrealized Losses	33	49
Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for sale, Amortized Cost	17	21
Available for sale, Gross Unrealized Gains	2	0
Available for sale, Gross Unrealized Losses	0	1
Available for sale, Fair Value	19	20
Held to maturities, Amortized Cost	15	15
Held to maturities, Gross Unrealized Gains	0	0
Held to maturities, Gross Unrealized Losses	0	0
Held to maturities, Fair Value	15	15
Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for sale, Amortized Cost	14,469	16,652
Available for sale, Gross Unrealized Gains	28	31
Available for sale, Gross Unrealized Losses	206	275
Available for sale, Fair Value	14,291	16,408
Held to maturities, Amortized Cost	8,216	8,404
Held to maturities, Gross Unrealized Gains	4	1
Held to maturities, Gross Unrealized Losses	149	173
Held to maturities, Fair Value	8,071	8,232
Other Mortgage-Backed Securities [Member] \| Agency Residential Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Held to maturities, Gross Unrealized Losses	4	5
Other Mortgage-Backed Securities [Member] \| Agency Commercial Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for sale, Amortized Cost	1,941	1,778
Available for sale, Gross Unrealized Gains	0	0
Available for sale, Gross Unrealized Losses	44	35
Available for sale, Fair Value	1,897	1,743
Held to maturities, Amortized Cost	1,777	1,184
Held to maturities, Gross Unrealized Gains	6	1
Held to maturities, Gross Unrealized Losses	33	49
Held to maturities, Fair Value	$ 1,750	$ 1,136

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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-Publisher FASB
-Name Accounting Standards Codification
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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount after other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

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