Consolidated Statements of Cash Flows (Parenthetical) - Secured Debt - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Feb. 28, 2019	Aug. 14, 2018
$108 Million Credit Facility
Maximum borrowing capacity	$ 108	$ 108	$ 108		$ 108
$495 Million Credit Facility
Maximum borrowing capacity	$ 495	$ 495	$ 495	$ 495

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant