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Investment Securities - Available-for-Sale Securities (Detail) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 78,600	$ 77,984
Allowance for Credit Losses	(5)
Gross Unrealized Gains	2,980	1,561
Gross Unrealized Losses	(152)	(332)
Fair Value	81,423	79,213
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	4,333	4,122
Allowance for Credit Losses	0
Gross Unrealized Gains	27	6
Gross Unrealized Losses	0	(4)
Fair Value	4,360	4,124
RMBS, Agency
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	62,126	62,003
Allowance for Credit Losses	0
Gross Unrealized Gains	2,434	1,120
Gross Unrealized Losses	(103)	(284)
Fair Value	64,457	62,839
RMBS, Non-agency
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,195	1,235
Allowance for Credit Losses	(5)
Gross Unrealized Gains	113	266
Gross Unrealized Losses	(19)	(2)
Fair Value	1,284	1,499
RMBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	63,321	63,238
Allowance for Credit Losses	(5)
Gross Unrealized Gains	2,547	1,386
Gross Unrealized Losses	(122)	(286)
Fair Value	65,741	64,338
CMBS, Agency
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	9,707	9,303
Allowance for Credit Losses	0
Gross Unrealized Gains	403	165
Gross Unrealized Losses	(26)	(42)
Fair Value	10,084	9,426
Other securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,239	1,321
Allowance for Credit Losses	0
Gross Unrealized Gains	3	4
Gross Unrealized Losses	(4)	0
Fair Value	$ 1,238	$ 1,325

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- Definition

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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