Commitments and Contingencies (Lawsuits) (Details) - Emergency Pricing And Consumer Protection Laws - Pending Litigation $ in Millions	12 Months Ended
Dec. 31, 2018 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
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14326-108349

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82911808&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
-Paragraph 9
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14557-108349

Name:	us-gaap_LossContingencyPeriodOfOccurrence
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration