Fair Value (Available-for-sale Securities) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis, Total	$ 98
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	(5)
Available-for-sale Securities	93	$ 252
Available-for-sale Securities, Amortized Cost Basis, Total		245
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		11
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		(4)
Available-for-sale Securities		252
Government [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis, Total	54
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	(3)
Available-for-sale Securities	51
Corporate [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis, Total	34
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	(2)
Available-for-sale Securities	32
Mortgage and Asset-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis, Total	10
Available-for-sale Securities	$ 10
Government and Corporate [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis, Total		189
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax		(4)
Available-for-sale Securities		185
Domestic [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Equity Securities, Amortized Cost Basis, Total		51
Available-for-sale Equity Securities, Accumulated Gross Unrealized Gain, before Tax		10
Available-for-sale Securities, Equity Securities		61
International [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Equity Securities, Amortized Cost Basis, Total		5
Available-for-sale Equity Securities, Accumulated Gross Unrealized Gain, before Tax		1
Available-for-sale Securities, Equity Securities		$ 6

Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) 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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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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).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in equity securities classified as available-for-sale.

+ References

No definition available.

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+ References

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

No definition available.

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+ References

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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).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26610-111562

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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Amount of equity securities categorized neither as held-to-maturity nor as trading.

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