Investment Securities - Available-for-Sale Securities (Details) - USD ($)	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Purchase of AFS securities	$ 500,000,000	$ 340,000,000	$ 904,000,000
Investment securities available-for-sale	2,116,000,000	2,142,000,000
AFS securities sold	432,000,000	$ 0
Gain on AFS securities	7,000,000
Other MBS
Debt Securities, Available-for-sale [Line Items]
Investment securities available-for-sale	$ 19,000,000
US Government-Sponsored Agency Securities
Debt Securities, Available-for-sale [Line Items]
AFS securities sold			289,000,000
Gain on AFS securities			$ 3,000,000

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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+ References

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Amount of realized gain (loss) 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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-Publisher FASB
-Name Accounting Standards Codification
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Amount of cash outflow to acquire 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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