Condensed Financial Statements - Dividends and Distributions (Details) - Parent Company [Member] - USD ($) $ in Millions	2 Months Ended	12 Months Ended
Feb. 23, 2018	Dec. 31, 2017
Distribution [Line Items]
Proceeds from dividends received		$ 3,000
Subsequent Event [Member]
Distribution [Line Items]
Proceeds from dividends received	$ 158

Dividends received on equity and other investments during the current period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 25
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3536-108585

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