Commitments and Contingencies - Environmental (Details) $ in Millions	3 Months Ended			12 Months Ended
	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Sep. 30, 2013 USD ($)	Dec. 31, 2015 USD ($) sites	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Loss Contingencies [Line Items]
Accrued obligations for environmental matters, current liabilities				$ 50	$ 60
Estimated time frame for accrued cost distributions				10 years
Environmental Issue
Loss Contingencies [Line Items]
Number of alleged environmental contamination sites (in sites) | sites				223
Number of environmental superfund sites (in sites) | sites				18
Liability for third-party tort claims				$ 12	15
Additional Expense Based on Actuarial Study Results	$ 7	$ 5	$ 12
Future costs for environmental liabilities, minimum				285
Future costs for environmental liabilities, maximum				500
Accrual for Environmental Loss Contingencies [Roll Forward]
Beginning balance				404	435	$ 458
Accruals				4	13	19
Payments				(39)	(44)	(42)
Ending balance				$ 369	$ 404	$ 435