Intangible Assets Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Indefinite-lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets Acquired	$ 16	$ 11
Impairment of Intangible Assets (Excluding Goodwill)	5	48
Amortization expense	$ 52	$ 60	$ 88