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Investment Securities - Investment Available for Sale (Detail) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 84,742	$ 77,984
Allowance for Credit Losses	(3)
Gross Unrealized Gains	3,211	1,561
Gross Unrealized Losses	(91)	(332)
Fair Value	87,859	79,213
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	4,353	4,122
Allowance for Credit Losses	0
Gross Unrealized Gains	12	6
Gross Unrealized Losses	(3)	(4)
Fair Value	4,362	4,124
RMBS, Agency
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	68,223	62,003
Allowance for Credit Losses	0
Gross Unrealized Gains	2,541	1,120
Gross Unrealized Losses	(77)	(284)
Fair Value	70,687	62,839
RMBS, Non-agency
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,144	1,235
Allowance for Credit Losses	(3)
Gross Unrealized Gains	187	266
Gross Unrealized Losses	(1)	(2)
Fair Value	1,327	1,499
RMBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	69,367	63,238
Allowance for Credit Losses	(3)
Gross Unrealized Gains	2,728	1,386
Gross Unrealized Losses	(78)	(286)
Fair Value	72,014	64,338
CMBS, Agency
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	9,940	9,303
Allowance for Credit Losses	0
Gross Unrealized Gains	469	165
Gross Unrealized Losses	(9)	(42)
Fair Value	10,400	9,426
Other securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,082	1,321
Allowance for Credit Losses	0
Gross Unrealized Gains	2	4
Gross Unrealized Losses	(1)	0
Fair Value	$ 1,083	$ 1,325

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Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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