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Investment Securities - Available-for-Sale Securities (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 77,984	$ 46,728
Gross Unrealized Gains	1,561	394
Gross Unrealized Losses	(332)	(972)
Fair Value	79,213	46,150
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	4,122	6,146
Gross Unrealized Gains	6	15
Gross Unrealized Losses	(4)	(17)
Fair Value	4,124	6,144
RMBS, Agency
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	62,003	32,710
Gross Unrealized Gains	1,120	62
Gross Unrealized Losses	(284)	(869)
Fair Value	62,839	31,903
RMBS, Non-agency
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,235	1,440
Gross Unrealized Gains	266	304
Gross Unrealized Losses	(2)	(2)
Fair Value	1,499	1,742
RMBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	63,238	34,150
Gross Unrealized Gains	1,386	366
Gross Unrealized Losses	(286)	(871)
Fair Value	64,338	33,645
CMBS, Agency
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	9,303	4,806
Gross Unrealized Gains	165	11
Gross Unrealized Losses	(42)	(78)
Fair Value	9,426	4,739
Other securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,321	1,626
Gross Unrealized Gains	4	2
Gross Unrealized Losses	0	(6)
Fair Value	$ 1,325	$ 1,622

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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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