Commitments and Contingencies - Other Lawsuits (Details) - Pending Litigation - Emergency Pricing And Consumer Protection Laws $ in Millions	6 Months Ended
Jun. 30, 2019 USD ($)
Loss Contingencies [Line Items]
Plaintiff	Commonwealth of Kentucky
Damages sought	$ 89
Loss contingency, period of occurrence	during September and October 2005

States when the existing condition, situation, or set of circumstances involving uncertainty occurred.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
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-URI http://asc.fasb.org/extlink&oid=118942415&loc=d3e14326-108349

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
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-URI http://asc.fasb.org/extlink&oid=118942415&loc=d3e14435-108349

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
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-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118942415&loc=d3e14557-108349

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