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Income Taxes (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended			12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Taxes [Abstract]
Federal statutory tax rate				21.00%	21.00%	21.00%
Income Tax Expense (Benefit), Continuing Operations, Adjustment of Deferred Tax (Asset) Liability		$ (21)	$ (31)
Total accrued liabilities for interest and penalties				$ 8	$ 3
Total interest and penalties recognized as part of income tax expense	$ 11			$ 5	$ (4)	$ (1)
Tax expense recognized as a part of income tax examination	10
Interest expense recognized as a part of income tax examination	$ 1
Income tax examination refund			$ 19

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- Definition

Refund for income taxes and interest from settlement with a taxing authority.

+ References

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- Definition

Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 6.I.Fact.4)
-URI http://asc.fasb.org/extlink&oid=116825942&loc=d3e330036-122817

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 12
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The amount of estimated interest recognized in the period arising from income tax examinations.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)
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The amount of estimated penalties and interest accrued as of the balance sheet date arising from income tax examinations.

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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
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The sum of the amounts of estimated penalties and interest recognized in the period arising from income tax examinations.

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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)
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The amount of estimated penalties recognized in the period arising from income tax examinations.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
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Amount of income tax expense (benefit) from continuing operations attributable to an adjustment of a deferred tax liability or asset for enacted changes in tax laws or rates or a change in the tax status of the entity.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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-Paragraph 9
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