Investments in Debt and Equity Securities (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Schedule of Investments in Debt and Equity Securities
Cost basis	$ 1,597	$ 1,340
Unrealized pretax net gains (losses)	63	25
Fair Value	1,660	1,365
U.S. treasury bonds
Schedule of Investments in Debt and Equity Securities
Cost basis	16	9
Unrealized pretax net gains (losses)	0	0
Fair Value	16	9
Other U.S. and non-U.S. government bonds
Schedule of Investments in Debt and Equity Securities
Cost basis	50	54
Unrealized pretax net gains (losses)	1	0
Fair Value	51	54
Corporate bonds
Schedule of Investments in Debt and Equity Securities
Cost basis	958	836
Unrealized pretax net gains (losses)	43	20
Fair Value	1,001	856
Asset-backed securities
Schedule of Investments in Debt and Equity Securities
Cost basis	156	62
Unrealized pretax net gains (losses)	2	0
Fair Value	158	62
U.S. governmental agency mortgage-backed securities
Schedule of Investments in Debt and Equity Securities
Cost basis	351	327
Unrealized pretax net gains (losses)	13	4
Fair Value	364	331
Residential
Schedule of Investments in Debt and Equity Securities
Cost basis	5	6
Unrealized pretax net gains (losses)	0	0
Fair Value	5	6
Commercial
Schedule of Investments in Debt and Equity Securities
Cost basis	61	46
Unrealized pretax net gains (losses)	4	1
Fair Value	$ 65	$ 47

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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
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-URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27161-111563

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=121558606&loc=SL82898722-210454

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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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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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