Derivative Instruments (Narrative) (Details) - USD ($)	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Derivative Instruments [Abstract]
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months	$ 29,000,000
Cash flow hedge, reclassified to earnings, net	0	$ 0
Non-performance Risk Adjustment	0
Exposure Associated With Collateralization Events	$ 0		$ 0

The estimated net amount of existing gains or losses on cash flow hedges at the reporting date expected to be reclassified to earnings within the next 12 months.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=112277219&loc=d3e80748-113994

Name:	us-gaap_CashFlowHedgeGainLossToBeReclassifiedWithinTwelveMonths
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration