Income Taxes, Deferred Tax Valuation Allowance (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred tax valuation allowance, rollfoward
Balance at beginning of year	$ 65
Balance at end of year	77	$ 65
Deferred tax asset valuation allowance
Deferred tax valuation allowance, rollfoward
Balance at beginning of year	65	55	$ 53
Charged to income tax expense	12	10	2
Balance at end of year	$ 77	$ 65	$ 55

Amount of increase in the allowances and reserves, which consist of the valuation and qualifying accounts that are either netted against the cost of an asset or that reflect a liability established to represent expected future costs, from charges to costs and expenses.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 4
-Subparagraph (SX 210.12-09)
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24092-122690

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration