Securities - Gross unrealized losses and related fair values (Detail) $ in Millions	Mar. 31, 2016 USD ($) security	Dec. 31, 2015 USD ($) security
Schedule of Available-for-sale Securities [Line Items]
Number of securities available for sale in one year or less \| security	55	287
Securities available-for-sale gross unrealized losses one year or less	$ (121)	$ (403)
Securities available-for-sale aggregate fair value of investment one year or less	$ 8,645	$ 22,754
Number of Securities available for sale greater than one year \| security	56	38
Securities available-for-sale gross unrealized losses greater than one year	$ (190)	$ (93)
Securities available-for-sale aggregate fair value of investment greater than one year	$ 2,868	$ 1,516
Number of securities held-to-maturity in one year or less \| security	97	458
Securities held-to-maturity gross unrealized losses one year or less	$ (1)	$ (36)
Securities held-to-maturity aggregate fair value of investment one year or less	$ 228	$ 4,446
Securities held-to-maturity greater than one year \| security	667	709
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	$ 38	$ 21
U.S. Treasury [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of securities available for sale in one year or less \| security	19	52
Securities available-for-sale gross unrealized losses one year or less	$ (68)	$ (227)
Securities available-for-sale aggregate fair value of investment one year or less	$ 3,548	$ 11,046
Number of Securities available for sale greater than one year \| security	22	5
Securities available-for-sale gross unrealized losses greater than one year	$ (133)	$ (43)
Securities available-for-sale aggregate fair value of investment greater than one year	$ 2,089	$ 924
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	20	164
Securities available-for-sale gross unrealized losses one year or less	$ (24)	$ (30)
Securities available-for-sale aggregate fair value of investment one year or less	$ 913	$ 1,451
Number of Securities available for sale greater than one year \| security	22	19
Securities available-for-sale gross unrealized losses greater than one year	$ (15)	$ (13)
Securities available-for-sale aggregate fair value of investment greater than one year	$ 330	$ 282
Number of securities held-to-maturity in one year or less \| security	15	312
Securities held-to-maturity gross unrealized losses one year or less	$ 0	$ (14)
Securities held-to-maturity aggregate fair value of investment one year or less	$ 1	$ 1,143
Securities held-to-maturity greater than one year \| security	47	49
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	$ 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	11	62
Securities available-for-sale gross unrealized losses one year or less	$ (28)	$ (141)
Securities available-for-sale aggregate fair value of investment one year or less	$ 4,004	$ 9,725
Number of Securities available for sale greater than one year \| security	3	3
Securities available-for-sale gross unrealized losses greater than one year	$ (7)	$ (8)
Securities available-for-sale aggregate fair value of investment greater than one year	$ 98	$ 101
Number of securities held-to-maturity in one year or less \| security	81	145
Securities held-to-maturity gross unrealized losses one year or less	$ (1)	$ (22)
Securities held-to-maturity aggregate fair value of investment one year or less	$ 227	$ 3,303
Securities held-to-maturity greater than one year \| security	617	657
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	$ 16	$ 20
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	3	4
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	$ 13	$ 16
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	$ 0
Securities available-for-sale aggregate fair value of investment greater than one year	$ 0	$ 45
Number of securities held-to-maturity in one year or less \| security	1	1
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	$ 9
Number of Securities available for sale greater than one year \| security	8	8
Securities available-for-sale gross unrealized losses greater than one year	$ (33)	$ (29)
Securities available-for-sale aggregate fair value of investment greater than one year	$ 162	$ 164
Foreign debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of securities available for sale in one year or less \| security	0	3
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	$ 0	$ 351
Number of Securities available for sale greater than one year \| security	1	0
Securities available-for-sale gross unrealized losses greater than one year	$ (2)	$ 0
Securities available-for-sale aggregate fair value of investment greater than one year	$ 189	$ 0
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	$ (1)	$ (3)
Securities available-for-sale aggregate fair value of investment one year or less	$ 158	$ 156
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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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.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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