Investments - Available-for-Sale (Details) $ in Millions	Dec. 31, 2020 USD ($) security	Dec. 31, 2019 USD ($) security
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	$ 77	$ 365
Unrealized Losses	$ 1	$ 2
Total Number of Positions \| security	21	239
Mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	$ 77	$ 143
Unrealized Losses	$ 1	$ 1
Total Number of Positions \| security	21	72
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	$ 0	$ 222
Unrealized Losses	$ 0	$ 1
Total Number of Positions \| security	0	167

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27337-111563

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
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-Section 55
-Paragraph 8
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Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=121582814&loc=SL82922890-210455

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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-Section 50
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Number of investments in debt securities measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without an allowance for credit loss. Includes beneficial interest in securitized financial asset.

+ References

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