Commitments and Contingent Liabilities - Additional information (Details) - USD ($) $ in Millions	1 Months Ended		3 Months Ended	12 Months Ended
	Nov. 30, 2013	Oct. 31, 2013	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Line of Credit Facility [Line Items]
Net rental expense under operating leases				$ 6	$ 8	$ 10
Surety bond, annual fee					$ 5	$ 7
Surety bond fees recovered during the period			$ (13)
Securities Litigation [Member]
Line of Credit Facility [Line Items]
Litigation judgment claims	$ 2,500	$ 2,500