Derivative Instruments - Derivatives and Hedges (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016 USD ($) MMBTU	Sep. 30, 2015 USD ($) MMBTU	Sep. 30, 2016 USD ($) MMBTU	Sep. 30, 2015 USD ($) MMBTU	Dec. 31, 2015 USD ($)
Commodity forward contracts | Cash Flow Hedges
Derivatives and Hedges
Coverage of commodity forward contracts (in MM BTUs) | MMBTU	12,400,000	6,300,000	12,400,000	6,300,000
Unrecognized (loss) gain included in Accumulated OCI	$ 2	$ 2	$ 2	$ 2	$ (4)
Commodity forward contracts gain (loss) recognized in OCI	(1)	2	2	2
Commodity forward contracts gain (loss) reclassified from accumulated OCI into income		4		6
Foreign exchange derivative contracts | Derivatives not designated as hedging instruments | Other Expenses.
Derivatives and Hedges
Foreign exchange contracts gain (loss) recognized in income	4	(4)	6	2
Forward exchange contracts | Derivatives not designated as hedging instruments
Derivatives and Hedges
Foreign exchange contracts in various currencies	$ 580	$ 600	$ 580	$ 600