Financial Instruments - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Cap agreement effective 1/1/17-12/31/18
Derivative [Line Items]
Interest rate cap, cap rate	1.50%
Notional amount	$ 1,400
Interest rate cap, fair value	5	$ 5
Interest Rate Contract
Derivative [Line Items]
Amount to be reclassified from AOCL to interest expense	5
Derivative
Derivative [Line Items]
Interest gain (loss) reclassified to earnings	$ 1	$ 3