Securities - Gross unrealized losses and related fair values (Detail) $ in Millions	Dec. 31, 2021 USD ($) security	Dec. 31, 2020 USD ($) security
Debt Securities, Available-for-sale [Line Items]
Number of securities available for sale in one year or less \| security	141	42
Securities available-for-sale gross unrealized losses one year or less	$ (276)	$ (29)
Securities available-for-sale aggregate fair value of investment one year or less	$ 18,168	$ 3,818
Number of Securities available for sale greater than one year \| security	41	31
Securities available-for-sale gross unrealized losses greater than one year	$ (86)	$ (43)
Securities available-for-sale aggregate fair value of investment greater than one year	$ 2,080	$ 1,566
U.S. Treasury
Debt Securities, Available-for-sale [Line Items]
Number of securities available for sale in one year or less \| security	11	5
Securities available-for-sale gross unrealized losses one year or less	$ (28)	$ (5)
Securities available-for-sale aggregate fair value of investment one year or less	$ 1,784	$ 751
Number of Securities available for sale greater than one year \| security	9	13
Securities available-for-sale gross unrealized losses greater than one year	$ (44)	$ (42)
Securities available-for-sale aggregate fair value of investment greater than one year	$ 856	$ 1,271
U.S. Government sponsored enterprises
Debt Securities, Available-for-sale [Line Items]
Number of securities available for sale in one year or less \| security	63	15
Securities available-for-sale gross unrealized losses one year or less	$ (155)	$ (3)
Securities available-for-sale aggregate fair value of investment one year or less	$ 6,224	$ 715
Number of Securities available for sale greater than one year \| security	14	8
Securities available-for-sale gross unrealized losses greater than one year	$ (12)	$ (1)
Securities available-for-sale aggregate fair value of investment greater than one year	$ 354	$ 46
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	59	13
Securities available-for-sale gross unrealized losses one year or less	$ (91)	$ (11)
Securities available-for-sale aggregate fair value of investment one year or less	$ 8,972	$ 1,482
Number of Securities available for sale greater than one year \| security	15	3
Securities available-for-sale gross unrealized losses greater than one year	$ (24)	$ 0
Securities available-for-sale aggregate fair value of investment greater than one year	$ 769	$ 8
Asset-backed securities
Debt Securities, Available-for-sale [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	$ (10)
Securities available-for-sale aggregate fair value of investment one year or less	$ 0	$ 104
Number of Securities available for sale greater than one year \| security	3	2
Securities available-for-sale gross unrealized losses greater than one year	$ (6)	$ 0
Securities available-for-sale aggregate fair value of investment greater than one year	$ 101	$ 0
Foreign debt securities
Debt Securities, Available-for-sale [Line Items]
Number of securities available for sale in one year or less \| security	8	6
Securities available-for-sale gross unrealized losses one year or less	$ (2)	$ 0
Securities available-for-sale aggregate fair value of investment one year or less	$ 1,188	$ 766
Number of Securities available for sale greater than one year \| security	0	5
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	$ 241

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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Number of investments in debt securities measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer, without an allowance for credit loss. Includes beneficial interest in securitized financial asset.

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