Financial Instruments - Terminated Swaps (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Amortization of fair value adjustments for terminated swaps	$ 19	$ 22	$ 31
Expected net decrease to interest expense in future years through 2018	$ 27