Investments - Unrealized Loss Position (Details) $ in Millions	Dec. 31, 2018 USD ($) security
Debt Securities, Available-for-sale [Line Items]
Number of securities \| security	2,279
Fair value	$ 2,409
Unrealized losses	$ 36
U.S. government securities
Debt Securities, Available-for-sale [Line Items]
Number of securities \| security	8
Fair value	$ 26
Unrealized losses	$ 0
States, municipalities and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Number of securities \| security	54
Fair value	$ 86
Unrealized losses	$ 1
U.S. corporate securities
Debt Securities, Available-for-sale [Line Items]
Number of securities \| security	1,399
Fair value	$ 1,431
Unrealized losses	$ 16
Foreign securities
Debt Securities, Available-for-sale [Line Items]
Number of securities \| security	243
Fair value	$ 314
Unrealized losses	$ 3
Residential mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Number of securities \| security	45
Fair value	$ 1
Unrealized losses	$ 0
Other asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Number of securities \| security	516
Fair value	$ 528
Unrealized losses	$ 15
Redeemable preferred securities
Debt Securities, Available-for-sale [Line Items]
Number of securities \| security	14
Fair value	$ 23
Unrealized losses	$ 1

Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale in a continuous loss position.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27337-111563

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- Definition

This item represents the aggregate fair value of investments in debt and equity securities in an unrealized loss position which are categorized neither as held-to-maturity nor trading securities.

+ References

No definition available.

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- Definition

Number of investment positions in available-for-sale investments in a continuous unrealized loss position for which an other-than-temporary impairment (OTTI) has not been recognized in the income statement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27290-111563

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- Definition

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.

+ References

No definition available.

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