Stock-Based Compensation (DSU - Details 3) - Deferred Stock Units - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Stock-Based Compensation
Balance outstanding at the beginning of the period (in units)	427,578
Balance outstanding at the beginning of the period, Weighted Average Grant-Date Fair Value per Unit (in dollars per unit)	$ 21.88
Granted (in units)	102,147
Granted, Weighted Average Grant-Date Fair Value per Unit (in dollars per unit)	$ 16.85	$ 25.14	$ 35.63
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period	(76,051)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value	$ 18.37
Balance outstanding at the end of the period (in units)	453,674	427,578
Balance outstanding at the end of the period, Weighted Average Grant-Date Fair Value per Unit (in dollars per unit)	$ 21.54	$ 21.88
Aggregate intrinsic value for DSUs outstanding	$ 6	$ 5	$ 10
Aggregate intrinsic values for DSUs converted to common stock during the period	$ 1	$ 0	$ 1