Investment Securities - Available-For-Sale Securities (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 24,003	$ 25,394
Gross Unrealized Gains	1,363	854
Debt Securities, Available-for-sale, Allowance for Credit Loss	0
Gross Unrealized Losses	(28)
Debt Securities, Available-for-sale	25,338	26,174
Accrued Interest Receivable	64
Agency
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	23,054	24,390
Gross Unrealized Gains	1,209	571
Debt Securities, Available-for-sale, Allowance for Credit Loss	0
Gross Unrealized Losses	(27)
Debt Securities, Available-for-sale	24,236	24,887
Accrued Interest Receivable	62
Non-agency and other
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	949	1,004
Gross Unrealized Gains	154	283
Debt Securities, Available-for-sale, Allowance for Credit Loss	0
Gross Unrealized Losses	(1)
Debt Securities, Available-for-sale	1,102	1,287
Accrued Interest Receivable	$ 2
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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