Additional Shareholders' Equity Information - Narrative (Details) $ in Millions	12 Months Ended
Dec. 31, 2018 USD ($)
Derivative [Line Items]
Stranded tax assets	$ 6
Interest Rate Contract
Derivative [Line Items]
Loss on derivative	$ 24

Amount of decrease in the fair value of derivatives recognized in the income statement.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4A
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5618551-113959

Name:	us-gaap_DerivativeLossOnDerivative
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration