Investment Securities - Schedule of Available-for-Sale Securities (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 46,728	$ 37,628
Gross Unrealized Gains	394	485
Gross Unrealized Losses	(972)	(458)
Fair Value	46,150	37,655
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	6,146	5,168
Gross Unrealized Gains	15	11
Gross Unrealized Losses	(17)	(8)
Fair Value	6,144	5,171
RMBS, Agency
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	32,710	26,013
Gross Unrealized Gains	62	67
Gross Unrealized Losses	(869)	(402)
Fair Value	31,903	25,678
RMBS, Non-agency
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,440	1,722
Gross Unrealized Gains	304	393
Gross Unrealized Losses	(2)	(1)
Fair Value	1,742	2,114
RMBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	34,150	27,735
Gross Unrealized Gains	366	460
Gross Unrealized Losses	(871)	(403)
Fair Value	33,645	27,792
CMBS, Agency
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	4,806	3,209
Gross Unrealized Gains	11	10
Gross Unrealized Losses	(78)	(44)
Fair Value	4,739	3,175
Other securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,626	1,516
Gross Unrealized Gains	2	4
Gross Unrealized Losses	(6)	(3)
Fair Value	$ 1,622	$ 1,517

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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Amount, before tax, of unrealized loss 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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Amount of 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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