Available-for-Sale Securities (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Jun. 30, 2020
Debt Securities, Available-for-sale [Line Items]
Available-for-sale debt securities, amortized cost basis	$ 18,708	$ 18,730
Available-for-sale debt securities, accumulated gross unrealized gain, before tax	903	1,354
Available-for-sale debt securities, accumulated gross unrealized loss, before tax	(110)	(92)
Available-for-sale debt securities, fair value	19,501	$ 19,992
Transfer of available-for-sale securities to held-to-maturity	$ 744
Credit card receivable [Member]
Debt Securities, Available-for-sale [Line Items]
Percentage of asset backed securities collateral	54.00%	40.00%
Auto loan receivable [Member]
Debt Securities, Available-for-sale [Line Items]
Percentage of asset backed securities collateral	18.00%	37.00%
Student loan receivable [Member]
Debt Securities, Available-for-sale [Line Items]
Percentage of asset backed securities collateral	28.00%	23.00%
Agency mortgage-backed securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale debt securities, amortized cost basis	$ 16,267	$ 14,567
Available-for-sale debt securities, accumulated gross unrealized gain, before tax	836	1,151
Available-for-sale debt securities, accumulated gross unrealized loss, before tax	(68)	(83)
Available-for-sale debt securities, fair value	17,035	15,635
Agency debentures [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale debt securities, amortized cost basis	632	1,210
Available-for-sale debt securities, accumulated gross unrealized gain, before tax	27	49
Available-for-sale debt securities, accumulated gross unrealized loss, before tax	0	(4)
Available-for-sale debt securities, fair value	659	1,255
US Treasuries [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale debt securities, amortized cost basis	1,233	1,202
Available-for-sale debt securities, accumulated gross unrealized gain, before tax	34	121
Available-for-sale debt securities, accumulated gross unrealized loss, before tax	(40)	0
Available-for-sale debt securities, fair value	1,227	1,323
Non-agency asset-backed securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale debt securities, amortized cost basis	417	1,479
Available-for-sale debt securities, accumulated gross unrealized gain, before tax	2	14
Available-for-sale debt securities, accumulated gross unrealized loss, before tax	(2)	(5)
Available-for-sale debt securities, fair value	417	1,488
Non-agency mortgage backed securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale debt securities, amortized cost basis	159	272
Available-for-sale debt securities, accumulated gross unrealized gain, before tax	4	19
Available-for-sale debt securities, accumulated gross unrealized loss, before tax	0	0
Available-for-sale debt securities, fair value	$ 163	$ 291

Represent the concentration risk of the asset backed securities collateral.

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- Definition

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+ References

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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).

+ References

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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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Amortized cost 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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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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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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