Debt - 4.50% Senior Exchangeable Notes issued August 2009 (Narrative) (Details) - Senior Exchangeable Notes due 2015 at a fixed interest rate of 4.50% - USD ($) $ in Millions	1 Months Ended
	Aug. 31, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Extinguishment of debt, amount	$ 131
Fixed interest rate	4.50%	4.50%	4.50%	4.50%