Investments (Unrealized Losses) (Details) - Debt securities	Dec. 31, 2018 security
Available-for-Sale Securities and Held-to-Maturity Securities [Line Items]
Number of securities with gross unrealized losses	653
Gross unrealized losses, percentage of total debt (in percentage)	50.60%
Gross unrealized losses, market value as a percent of amortized cost (in percentage)	96.80%
Number of securities with gross unrealized losses with maturities of 12 months or greater	195
Gross unrealized losses, number of securities with maturities of 12 months or greater (in percentage)	29.90%
External Credit Rating, Investment Grade
Available-for-Sale Securities and Held-to-Maturity Securities [Line Items]
Gross unrealized losses, number of securities rated investment grade	644

Available-for-Sale Securities and Held-to-Maturity Securities [Line Items]

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Available-for-sale Securities, Gross Unrealized Losses, Market Value of Bonds Percent of Amortized Cost

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Available-for-sale Securities, Gross Unrealized Losses, Number of Securities, Debt Maturities, Twelve Months or Greater, Percent of Total

+ References

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Available for Sale Securities, Gross Unrealized Losses, Number of Securities as a Percentage of Total Debt

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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 12 months or longer.

+ References

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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 unrealized loss position.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563

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Disclosure regarding factors used to determine that the impairment of securities categorized as held-to-maturity where cost exceeds fair value is not an other than temporary impairment (OTTI). This item contains disclosure of the number of investment positions in the held-to-maturity investments determined to be temporarily impaired.

+ 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=82897076&loc=d3e27290-111563

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