Investment Securities - Available-For-Sale Securities (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 20,635	$ 25,394
Gross Unrealized Gains	1,513	854
Debt Securities, Available-for-sale, Allowance for Credit Loss	0
Gross Unrealized Losses	(4)
Debt Securities, Available-for-sale	22,144	26,174
Accrued Interest Receivable	59
Agency
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	19,757	24,390
Gross Unrealized Gains	1,285	571
Debt Securities, Available-for-sale, Allowance for Credit Loss	0
Gross Unrealized Losses	(4)
Debt Securities, Available-for-sale	21,038	24,887
Accrued Interest Receivable	55
Non-agency and other
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	878	1,004
Gross Unrealized Gains	228	283
Debt Securities, Available-for-sale, Allowance for Credit Loss	0
Gross Unrealized Losses	0
Debt Securities, Available-for-sale	1,106	1,287
Accrued Interest Receivable	$ 4
Other-than-temporary impairment
Debt Securities, Available-for-sale [Line Items]
Gross Unrealized Losses		0
Other-than-temporary impairment \| Agency
Debt Securities, Available-for-sale [Line Items]
Gross Unrealized Losses		0
Other-than-temporary impairment \| Non-agency and other
Debt Securities, Available-for-sale [Line Items]
Gross Unrealized Losses		0
Temporary impairment
Debt Securities, Available-for-sale [Line Items]
Gross Unrealized Losses		(74)
Temporary impairment \| Agency
Debt Securities, Available-for-sale [Line Items]
Gross Unrealized Losses		(74)
Temporary impairment \| Non-agency and other
Debt Securities, Available-for-sale [Line Items]
Gross Unrealized Losses		$ 0

Interest, dividends, rents, ancillary and other revenues earned but not yet received by the entity on its investments.

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