Investment Securities - Schedule of Available-for-Sale Securities (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 45,872	$ 46,728
Gross Unrealized Gains	592	394
Gross Unrealized Losses	(296)	(972)
Fair Value	46,168	46,150
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	4,173	6,146
Gross Unrealized Gains	3	15
Gross Unrealized Losses	(21)	(17)
Fair Value	4,155	6,144
RMBS, Agency
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	33,727	32,710
Gross Unrealized Gains	239	62
Gross Unrealized Losses	(253)	(869)
Fair Value	33,713	31,903
RMBS, Non-agency
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,313	1,440
Gross Unrealized Gains	300	304
Gross Unrealized Losses	(1)	(2)
Fair Value	1,612	1,742
RMBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	35,040	34,150
Gross Unrealized Gains	539	366
Gross Unrealized Losses	(254)	(871)
Fair Value	35,325	33,645
CMBS, Agency
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	5,368	4,806
Gross Unrealized Gains	48	11
Gross Unrealized Losses	(20)	(78)
Fair Value	5,396	4,739
Other securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,291	1,626
Gross Unrealized Gains	2	2
Gross Unrealized Losses	(1)	(6)
Fair Value	$ 1,292	$ 1,622

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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