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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
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Summary of Accounting Policies Summary of Accounting Policies (Management Compensation Plans Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions		12 Months Ended
	Jan. 01, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, par value		$ 0.0001
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		3 years
Range of number of shares that will vest		zero to stretch
Director [Member] \| RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		1 year
Employee [Member] \| RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		3 years
Series A common stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, par value		$ 0.0001	$ 0.0001
Retained Earnings [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Cumulative Effect on Retained Earnings, Net of Tax	$ 1	$ (1)	$ 0	$ 0