Basis of Presentation and Significant Accounting Policies Measurement of Credit Losses on Financial Instruments (Details) - USD ($) $ in Thousands |
Jan. 01, 2020 |
Dec. 31, 2019 |
Dec. 31, 2018 |
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| Basis of Presentation and Significant Accounting Policies [Abstract] | |||
| Available-for-sale securities, amortized cost | $ 30,711,157 | $ 25,432,158 | |
| Estimated allowance for credit losses on available-for-sale debt securities upon adoption of ASU 2016-13 | $ 244,900 |
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- Definition Basis of Presentation and Significant Accounting Policies [Abstract] No definition available.
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- Definition Amortized cost 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
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- Definition Amount of allowance for credit loss 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
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