Segment Information (Long-Lived Assets By Geographic Area) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Long-Lived Assets [Line Items]
Long-lived Assets	$ 1,314	$ 1,394
North America [Member]
Long-Lived Assets [Line Items]
Long-lived Assets	420	436
Europe [Member]
Long-Lived Assets [Line Items]
Long-lived Assets	110	105
Rest of World [Member]
Long-Lived Assets [Line Items]
Long-lived Assets	$ 784	$ 853