Securities - Gross unrealized losses and related fair values (Detail) $ in Millions	Dec. 31, 2015 USD ($) security	Dec. 31, 2014 USD ($) security
Schedule of Available-for-sale Securities [Line Items]
Number of securities available for sale in one year or less \| security	287	79
Securities available-for-sale gross unrealized losses one year or less	$ (403)	$ (80)
Securities available-for-sale aggregate fair value of investment one year or less	$ 22,754	$ 7,745
Number of Securities available for sale greater than one year \| security	38	73
Securities available-for-sale gross unrealized losses greater than one year	$ (93)	$ (55)
Securities available-for-sale aggregate fair value of investment greater than one year	$ 1,516	$ 3,441
Number of securities held-to-maturity in one year or less \| security	458	247
Securities held-to-maturity gross unrealized losses one year or less	$ (36)	$ (3)
Securities held-to-maturity aggregate fair value of investment one year or less	$ 4,446	$ 1,379
Securities held-to-maturity greater than one year \| security	709	850
Securities held-to-maturity gross unrealized losses greater than one year	$ 0	$ 0
Securities held-to-maturity aggregate fair value of investment greater than one year	$ 21	$ 3
U.S. Treasury [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of securities available for sale in one year or less \| security	52	6
Securities available-for-sale gross unrealized losses one year or less	$ (227)	$ (47)
Securities available-for-sale aggregate fair value of investment one year or less	$ 11,046	$ 3,459
Number of Securities available for sale greater than one year \| security	5	4
Securities available-for-sale gross unrealized losses greater than one year	$ (43)	$ (11)
Securities available-for-sale aggregate fair value of investment greater than one year	$ 924	$ 1,546
US Government sponsored enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of securities available for sale in one year or less \| security	164	2
Securities available-for-sale gross unrealized losses one year or less	$ (30)	$ (1)
Securities available-for-sale aggregate fair value of investment one year or less	$ 1,451	$ 128
Number of Securities available for sale greater than one year \| security	19	24
Securities available-for-sale gross unrealized losses greater than one year	$ (13)	$ (6)
Securities available-for-sale aggregate fair value of investment greater than one year	$ 282	$ 391
Number of securities held-to-maturity in one year or less \| security	312	144
Securities held-to-maturity gross unrealized losses one year or less	$ (14)	$ (1)
Securities held-to-maturity aggregate fair value of investment one year or less	$ 1,143	$ 394
Securities held-to-maturity greater than one year \| security	49	47
Securities held-to-maturity gross unrealized losses greater than one year	$ 0	$ 0
Securities held-to-maturity aggregate fair value of investment greater than one year	$ 0	$ 0
US Government agency issued or guaranteed [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of securities available for sale in one year or less \| security	62	30
Securities available-for-sale gross unrealized losses one year or less	$ (141)	$ (20)
Securities available-for-sale aggregate fair value of investment one year or less	$ 9,725	$ 2,046
Number of Securities available for sale greater than one year \| security	3	10
Securities available-for-sale gross unrealized losses greater than one year	$ (8)	$ (9)
Securities available-for-sale aggregate fair value of investment greater than one year	$ 101	$ 213
Number of securities held-to-maturity in one year or less \| security	145	103
Securities held-to-maturity gross unrealized losses one year or less	$ (22)	$ (2)
Securities held-to-maturity aggregate fair value of investment one year or less	$ 3,303	$ 985
Securities held-to-maturity greater than one year \| security	657	800
Securities held-to-maturity gross unrealized losses greater than one year	$ 0	$ 0
Securities held-to-maturity aggregate fair value of investment greater than one year	$ 20	$ 2
Obligations of U.S. states and political subdivision [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of securities available for sale in one year or less \| security	4	34
Securities available-for-sale gross unrealized losses one year or less	$ 0	$ (2)
Securities available-for-sale aggregate fair value of investment one year or less	$ 16	$ 146
Number of Securities available for sale greater than one year \| security	3	23
Securities available-for-sale gross unrealized losses greater than one year	$ 0	$ (2)
Securities available-for-sale aggregate fair value of investment greater than one year	$ 45	$ 194
Number of securities held-to-maturity in one year or less \| security	1	0
Securities held-to-maturity gross unrealized losses one year or less	$ 0	$ 0
Securities held-to-maturity aggregate fair value of investment one year or less	$ 0	$ 0
Securities held-to-maturity greater than one year \| security	3	3
Securities held-to-maturity gross unrealized losses greater than one year	$ 0	$ 0
Securities held-to-maturity aggregate fair value of investment greater than one year	$ 1	$ 1
Asset backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of securities available for sale in one year or less \| security	1	1
Securities available-for-sale gross unrealized losses one year or less	$ 0	$ 0
Securities available-for-sale aggregate fair value of investment one year or less	$ 9	$ 3
Number of Securities available for sale greater than one year \| security	8	9
Securities available-for-sale gross unrealized losses greater than one year	$ (29)	$ (24)
Securities available-for-sale aggregate fair value of investment greater than one year	$ 164	$ 199
Foreign debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of securities available for sale in one year or less \| security	3	5
Securities available-for-sale gross unrealized losses one year or less	$ (2)	$ (9)
Securities available-for-sale aggregate fair value of investment one year or less	$ 351	$ 1,805
Number of Securities available for sale greater than one year \| security	0	3
Securities available-for-sale gross unrealized losses greater than one year	$ 0	$ (3)
Securities available-for-sale aggregate fair value of investment greater than one year	$ 0	$ 898
Equity securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of securities available for sale in one year or less \| security	1	1
Securities available-for-sale gross unrealized losses one year or less	$ (3)	$ (1)
Securities available-for-sale aggregate fair value of investment one year or less	$ 156	$ 158
Number of Securities available for sale greater than one year \| security	0	0
Securities available-for-sale gross unrealized losses greater than one year	$ 0	$ 0
Securities available-for-sale aggregate fair value of investment greater than one year	$ 0	$ 0

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Available for sale securities continuous unrealized loss position twelve months or longer number of securities.

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Held to maturity securities continuous unrealized loss position less than twelve months number of securities.

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Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for less than twelve months.

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This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for less than twelve months.

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