Securities Available for Sale - Realized gains/losses (Details) - USD ($)	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Schedule of Securities Available-for-Sale [Line Items]
Other-than-temporary impairment charges	$ 3,600,000	$ 3,000,000.0	$ 1,500,000
Credit losses recognized into earnings for OTTI securities	0	0	0
Proceeds	12,548,000	497,000	125,522,000
Gross realized gains	9,000	1,000	196,000
Gross realized losses	(1,000)	(3,000)	(26,000)
Other asset-backed securities
Schedule of Securities Available-for-Sale [Line Items]
Proceeds	4,500,000,000	2,000,000,000.0	831,100,000
Realized gain (loss) from asset-backed securities related to Structured Program transactions	$ 0	$ 0	$ 0

Amount of realized gain on 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
-Topic 320
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-Section 50
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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).

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Amount of realized loss 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 other-than-temporary impairment (OTTI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), recognized in earnings and other comprehensive loss (OCI).

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Amount of cash inflow from sale 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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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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