Securities - Gross unrealized losses and related fair values (Detail) $ in Millions	Mar. 31, 2022 USD ($) security	Dec. 31, 2021 USD ($) security
Debt Securities, Available-for-sale [Line Items]
Number of securities available for sale in one year or less \| security	405	141
Securities available-for-sale gross unrealized losses one year or less	$ (994)	$ (276)
Securities available-for-sale aggregate fair value of investment one year or less	$ 20,251	$ 18,168
Number of Securities available for sale greater than one year \| security	86	41
Securities available-for-sale gross unrealized losses greater than one year	$ (527)	$ (86)
Securities available-for-sale aggregate fair value of investment greater than one year	$ 5,748	$ 2,080
U.S. Treasury
Debt Securities, Available-for-sale [Line Items]
Number of securities available for sale in one year or less \| security	25	11
Securities available-for-sale gross unrealized losses one year or less	$ (78)	$ (28)
Securities available-for-sale aggregate fair value of investment one year or less	$ 4,007	$ 1,784
Number of Securities available for sale greater than one year \| security	14	9
Securities available-for-sale gross unrealized losses greater than one year	$ (83)	$ (44)
Securities available-for-sale aggregate fair value of investment greater than one year	$ 1,431	$ 856
U.S. Government sponsored enterprises
Debt Securities, Available-for-sale [Line Items]
Number of securities available for sale in one year or less \| security	253	63
Securities available-for-sale gross unrealized losses one year or less	$ (276)	$ (155)
Securities available-for-sale aggregate fair value of investment one year or less	$ 5,659	$ 6,224
Number of Securities available for sale greater than one year \| security	52	14
Securities available-for-sale gross unrealized losses greater than one year	$ (372)	$ (12)
Securities available-for-sale aggregate fair value of investment greater than one year	$ 3,472	$ 354
U.S. Government agency issued or guaranteed
Debt Securities, Available-for-sale [Line Items]
Number of securities available for sale in one year or less \| security	115	59
Securities available-for-sale gross unrealized losses one year or less	$ (632)	$ (91)
Securities available-for-sale aggregate fair value of investment one year or less	$ 9,486	$ 8,972
Number of Securities available for sale greater than one year \| security	16	15
Securities available-for-sale gross unrealized losses greater than one year	$ (62)	$ (24)
Securities available-for-sale aggregate fair value of investment greater than one year	$ 712	$ 769
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Number of securities available for sale in one year or less \| security	3	0
Securities available-for-sale gross unrealized losses one year or less	$ (1)	$ 0
Securities available-for-sale aggregate fair value of investment one year or less	$ 17	$ 0
Number of Securities available for sale greater than one year \| security	3	3
Securities available-for-sale gross unrealized losses greater than one year	$ (9)	$ (6)
Securities available-for-sale aggregate fair value of investment greater than one year	$ 97	$ 101
Foreign debt securities
Debt Securities, Available-for-sale [Line Items]
Number of securities available for sale in one year or less \| security	9	8
Securities available-for-sale gross unrealized losses one year or less	$ (7)	$ (2)
Securities available-for-sale aggregate fair value of investment one year or less	$ 1,082	$ 1,188
Number of Securities available for sale greater than one year \| security	1	0
Securities available-for-sale gross unrealized losses greater than one year	$ (1)	$ 0
Securities available-for-sale aggregate fair value of investment greater than one year	$ 36	$ 0

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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