Debt (Senior Note Offering) (Narrative) (Details) - USD ($)	12 Months Ended
Dec. 31, 2019	Jun. 30, 2006
Debt Instrument [Line Items]
Debt Instrument, Face Amount		$ 850,000,000
Senior Notes Due 2029 [Member]
Debt Instrument [Line Items]
Debt Instrument, Offering Date	May 15, 2019
Debt Instrument, Interest Rate, Stated Percentage	3.90%
Debt Instrument, Face Amount	$ 600,000,000
Proceeds from Debt, Net of Issuance Costs	594,000,000
Debt Related Commitment Fees and Debt Issuance Costs	$ 5,000,000
Senior Notes Due 2019 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	6.45%
Debt Instrument, Face Amount	$ 400,000,000

Face (par) amount of debt instrument at time of issuance.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
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-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399

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Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

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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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- Definition

Date the debt instrument was offered for sale, in CCYY-MM-DD format.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
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- Definition

Represents the charge against earnings during the period for commitment fees and debt issuance expenses.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
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-URI http://asc.fasb.org/extlink&oid=116634182&loc=SL114868664-224227

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- Definition

The cash inflow from additional borrowings, net of cash paid to third parties in connection with debt origination.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
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